We are on Campaign Two of our group. I DM'd campaign one, am now playing. I was new to DMing and so I had inadvertently given our characters some gear that they were pretty underleveled to really deserve. Including, a homebrew paladin sword. I thought the Sun Sword was really cool, but thought it was too powerful for a level 5 paladin. So after some consulting, we decided to make it just double smite damage. I thought, he can only smite a few times a day, and it won't really wind up being that much damage. I WAS WRONG.

So Campaign Two, same party, new DM (also first time DMing). He wanted to still make it challenging for us, but wound up making really mundane encounters that were outrageously difficult. Thing, a few Tabaxi bandits being able to present an actual threat to a suped-out party of 5. Well, one of the players got tired of his character and so arranged for a death with the DM. My character was the newest to the party and so was trying to make friends with everything and went out on the suicide mission, unaware it was a suicide mission. Eventually, I figured it out, and was cool about it so we let my character die too.

My next character was a very flavorful "time-wizard" (divination wizard) inspired by Howl from Howl's Moving Castle. But mega-amped on the paranoia/always running away bit. I eventually figured out that because of lucky feat, and portent rolls, I could force enemies to fail saving throws. I figured out that Hold Person on a forced failed save, could essentially give our Double Smite Paladin auto-crits. Doubled power Auto-crit. Over 100 damage in a single turn. Cool. But of course, this causes our DM in a very well-intentioned attempt to homebrew the monsters to be even more dangerous (again including the mundane ones like tabaxi bandits). So we kind of entered into a arms race of min-maxing and DM raising the stakes, which unfortunately led to a player vs DM mentality (really my fault).

Well, still under the impression that the DM was excited to work with my character's backstory/etc, I really go out of my way to play whole, mistrustful, on the run, paranoia deal. Not against the party of course. The DM introduces an actual psychopathic professional assassin that is going to be traveling with our party. I'm like "why are we letting this actual psychopathic professional assassin traveling with our party?" Especially since my character has pissed off a lot of important, powerful people. So no way he is going to trust an actual psychopathic professional assassin. I go to the rest of the players OOC and say "Here's the thing. Phineas is gonna be super freaked out and paranoid. I as a player, am also convinced that this guy is going to betray us. So Phineas is going to try to convince the others to kill actual psychopathic professional assassin in his sleep." The players agree that this is good plan. I let the DM know this is going to be our plan, in case actual psychopathic professional assassin is going to be story essential. He does not object to our plan. So in character, Phineas (my min-maxed time wizard), convinces the Double Smite Paladin to Double Smite actual psychopathic professional assassin in his sleep.

He gets double smited, extra attack, double smited again. Like 150 damage. The actual psychopathic assassin jumps up, destroys our most powerful character in two rounds. We dealt around 350ish damage to him, before deciding to flee and the DM (this assassin had like 21 AC btw) let's us know that the actual psychopathic assassin was not even "bloodied" (our term for half-hp). Through a combination of being whooped on by god-tier assassin, psychological horror and terror, trauma, etc. we wound up losing three party characters that night. Including my min-max time wizard, the double smite paladin, and the party druid (who really had more trauma in his life than anyone deserves). Apparently, we were not supposed to fight him YET, but after we had got the McGuffin that would allow us to fight on his level or something like that.

Of course, for a long time we were all really salty, but we eventually got over it as its a really good story, and led to the creation of some really cool characters.

TL;DR: I lost a character to a pre-arranged suicide mission that I did not realize was a suicide mission, accidentally started the min-maxing cold war, and caused three PC deaths in a fight featuring a demigod assassin that had no indication of being stronger than a tarrasque.

So many fun ones.

OLD 1st Edition game, my cleric and his group managed to survive an impossible encounter in the wilds, pitting their group of 6 against a warband of 14(!) homebrewed lizardfolk and coming out relatively unscathed. He was then bitten by a garden variety jungle snake and died of poison on his way back to the village to recover.

Out of the Abyss 5E, my dwarven incel neckbeard barbarian irritated one too many females and eventually got his throat slit during the night upon reaching Gracklstugh. (This was planned with the DM though, to be fair. I just couldn't keep roleplaying someone so verbally and socially abrasive).

During SKT, in one particular invasion with two fire giants stomping their way into town, my divination wizard tried to burn his ace immediately and use one of his portents to force the giant to fail its saving throw on a Suggestion spell... Which would have been amazing until the DM described what happened next. "You watch as the giant looks briefly confused before picking you up and hurling you through a nearby building... It doesn't understand Common."

Not one of my characters but too good not to mention: a ranger in my group was told of a nearby grove that was revered by nature lovers and worshipers of his deity. The NPC casually mentions that sometimes people don't come back from pilgrimages in the woods. Everyone else in the party is skeptical and asks if they believe people are being killed in the woods to which the NPC responds: "We never found any bodies, so *shrug*". Warning signs go off non stop in my head, being an analytical wizard/knowledge cleric. Ok, so the time to bed down for the night comes in this settlement and two of us chill out in the mid-range inn towards the center of town, one goes for the high dollar suite in the lodgings at the center of town. Our glorious ranger friend however decides its an excellent opportunity to go camping in the aforementioned grove. Alone. At night. With his closest allies being a mile away and not knowing his plan to do so... Fast forward to his "attempt" to rest... The DM describes a vision of his deity striding slowly through the woods towards him and asks him several times "What are you doing?" "He's picking up speed, what are you doing?" to which our friend responds: "Meditating. Waiting." He's now on top of him and drops his form, revealing an oni. Level 5 solo ranger did not stand much chance.

We were in a Gamma World campaign. I had joined late, and ended up taking over an abandoned character instead of creating my own. After playing him for awhile, I I made the mistake of mentioning to the DM that I would like to create a new character. Shortly after that, we're exploring an ancient ruin full of advanced tech. A very friendly service robot that has been inhabiting the place for a couple of centuries offers to upgrade us with cybernetic enhancements.

I thought, "Sure, why not!?" So I go for the increased natural armor enhancement to boost my AC. 

He gets me in the operating chair, and the DM gets very descriptive about how everything works, enthusiastically roleplaying the robot's mannerisms as he jauntily punches all the buttons on the panel. A sort of gel comes out and surrounds me, while the robot is turning knobs, lasers come on and begin cutting through my character's skin, presumably to insert whatever technological miracle is going to make me tougher. 

But no. The robot's friendly attitude notwithstanding, he has actually gone quite mad while living in this place and turned homicidal. The lasers slice and dice until I'm cut to ribbons. He then shuts down the machine, the gel recedes, and I spill out onto the floor like a very large can of diced tomatoes. 

It was so hilarious, I wasn't even mad--and I got to roll up that new character much sooner than expected.   

we're in a libary with 5 floors.
the druid decides to transform into a giant spider.
she comes in scares everyone.
my barbarian minotaur just imagine a monster coming in, he rushes to attack her.
she runs up to the second floor. i jump and grab the ledge of the second floor make my way up there. she walks back down. i jump down, taking 1d6 falling damage while raging. she climbs up and just runs up to the third floor. i jump ledge from ledge after her, she walks down the window outside the tower. i literally just jump down all 3 floor to her. taking 3d6 falling damage. she tries to run in the nearby forest, but my barbarian speed is higher then hers. and thus i get to her. i finally just attacks her a lot because 3 attacks. and she transforms back into her true form. she tries to talk me out of it. but i kill her as my characters is raging and while raging he's having problems of remembering whos who. once she's dead, my character chops her head off and comes back to the library saying he slew the beast and shows the head of the druid ! to which he realises who that head is and he says "OOOOooooh nooo" looks at the others of the party and the i get killed by the wizard magic missile level 2. i was on deaths door anyway. level 3 characters even with rage all those fall damage hurted much. its ok, i'm a zealot and they can rez me thanks to a witch they know.

to note, this was an evil campaign. my minotaur was praying a trickster goddest who wanted to be known so her power could up her rank within the deities rankings.

Another story...
in my current campaign we have a warforged and an old human lady.  we created an archetype for the wizard granny. in that archetype she can rez someone with only a certain percentage of chance of suceeding. we clal it the car battery jumper cables. because she holds that car battery sized resurecting machine. the warforged was badly damaged, he was glitching badly as he is a time traveler from the far future where mankind do not exists anymore. the world faces extinction and he wanna know why. not knowing why the creature is glitching (aka its translocator core which allows time travel is broken and cracked. its also his energy core on which he runs on). so the first great idea that granny player had was to reanimate the warforged even though he's already alove, just glitching for unknown reasons. she takes her car battery and boost the **** out of the warforged. i was expecting her to do some mending or whatever... but... yeah... the warforged core exploded from inside ! the stare the whole group did to the granny player was priceless. little did they know that the player who was playing the warforged couldn't be there for a whle, and thus i already had the idea of returning him into some kind of time travel trip to find his way back. and thus gone was the warforged. the group literally thought they had killed the player, as when he came back for a session or two before going back out for a while. he had a new character. it was ridiculous... the reasoning from that granny player was, he works on energy so i boosted him. and we were like, yeah... you boosted a damaged core. what the hell did you expect else to happen ? i mean boosting a ripped open battery will blow it up in your face. eventually, in hindsight, even him found him funny and the warforged player wasn't ad at all, he found it very very very funny !

No one died in this encounter, but we all came pretty darn close.

So, we were pretty low level, and we came upon this red dragon.  Combat is unavoidable, and we are getting wrecked.  The dragon swallows our ranger whole, and carries our rogue way up into the sky to drop him and kill him.  Me (a druid), a fighter, and an unconscious wizard are on the ground, watching the dragon rise higher and higher with two of our players.  

The Ranger, still conscious and unaware that the dragon has flown so high bursts out of the dragon's mouth.  Before he falls away, he manages to wrap his spiked chain around the dragon's neck and hold on.  The dragon, now being choked by said chain, drops our rogue and begins slowly struggling and falling as it loses air.  Fighter is just screaming and hoping for the best at this point.  Little old 3rd-level druid me is watching this and thinking "OH CRAP." because I have NO SPELLS that could help with this situation.

Unless...

I propose something so crazy that absolutely no logical interpretation of the rules would let me do it, but something that, if it works, might just save our puny lives.

"Roll a D20."

I role once, and fail.  My turn comes again.  I don't have that much time left.

Nat 20.

I cast entangle.  On the dragon.  The vines shoot out of the earth, hundreds of feet into the air, catch both of my players safely, and break the flipping red dragon's neck.My character collapses, totally unconscious from the effort of casting the spell.

As you can tell, that particular DM didn't put much stock in the rules.  One of our players once screamed "SPACE PIRATES" and because we got a Nat 20 space pirates came down and blasted our enemy.  The funnest campaign I have ever played.  By far.

this was in waterdeep dragon heist, we just fought the gold dragon and i was making death saves (i was a warlock of the fiend) and the blood hunter tried to heal me by pouring holy water down my throat. since i worshipped a devil, the DM made it so that the holiness and goodness of the water burned a hole in my evil throat and killed me. when i was resurrected, i still had the hole in my throat so i couldnt speak, and a cultist cut off my hand. i got a parrot to speak for me, but then moved my soul into the parrot and abandoned my human form. i got a blacksmith to make me a huge mech suit out of adamantine, so i was like a big golem but secretely a parrot under the mech suit.

excessive cheese consumption

As the DM this was my favorite idiot moment. 

Background:

Players survived through war after war, crowning a queen, defeating an adult dragon to free a people, cutting down a horde of demons, and finally holding the capital of the human lands from an army of dark dwarves. The army numbered 100,000, the players had 500 men left in the city. The battle was hopelesss so they had a spell that grew with every kill it got, and managed to kill enough that it wiped out the entire city while they hid in a pocket dimension one of them created with a spell i forget. After becoming heros, the king of the gods summoned them before him. They had managed to slay the song of a god who was now very angry. He wanted justice and complained to the king of the gods.

The king of gods gave them an option, after being locked into a room they were told to either step out with a black rock and choose the god they wished to challenge, bring out a white rock and accept the king of the gods as their chosen god and serve him and him alone. Or stay in the room and vanish from existence to be reborn. 

Idiot player: what would happen if i walked out with both rocks. Me: You shouldn't, the king of the gods is typically a very direct and non bullshit god. 

Idiot player: *walks out with both rocks in each hand* 

King of the Gods decided to wipe his existance from the world, and thanos snapped him in a very detailed and painful way. 

Idiot player: Why did he do that?

His entire party just glared at him for his stupidity. 

We did almost have someone die on Sunday during our Descent Into Avernus session after coming into contact with Yellow Mould.

 I died when some elderly man mistook me for cheese, an turned me into one

my minotaur once met guards at a tower belonging to a witch, she was fingering some of them once in a while. they were trying to get in to kill her.
i decided to stop the attack and talk to the lady. a finger of death later, i became a skeleton minotaur for her. which once she realised the minotaur part, she resurected me to be a good specimen. it was even better as she realised i was a zealot and it costed her nothing to rez me.

ok... this thread isn't about who got the best death ever though... but ok...
also... being turned into cheese is like... the most common way to die though...

also once my level 1 wizard was killed when an old lady rolled a critical hit for throwing a pebble at me

I've only ever lost one character, so I guess it qualifies as the dumbest way I died.

Basically, it was a ship-to-ship combat and my guy was a party of a reverse boarding party. Near the end of the fight, both sides with severe losses, our bard decided to use "Heat Metal" on one of the rival pirate's guns, which cause the gunpowder in it to explode, which caused the black powder bags he was carrying to explode, which cause our nearby gunslinger's powder to blow, which caused a cannon to blow, which caused the gun powder barrels on the ship to explode. 
The explosion did overall 206 points of fire damage to everyone on the ship, killing my warlock/paladin instantly. It was a glorious sign of cause and effect, the chain reaction won us the fight with only two player deaths. We won, but my guy only had 47 HP max and was killed instantly by the final explosion, unable to make it to the end of the ship and leap off to safety.

I've mostly DMed so I haven't had many opportunities to die, but my best one is: I walked too close to the window in the ruins of a castle, and apparently a dragon was on the other side and ate me in one gulp.

My 10th level Paladin-Warlock decided it was a great idea to misty step onto a beholder and grab on to its tentacles (he had acquired a reckless personality flaw). Sadly, neither of those tentacles was the petrification ray. Two failed saves later, he's a statue buried somewhere in the Lost City of Omu.

Disguise kit. Being too effective. And your party’s rogue is a murderhobo.

no “hey why did you look at us 3-5 times at that party then follow us” just straight. Murderhobo.

Quote from WildAlegoo >>

also once my level 1 wizard was killed when an old lady rolled a critical hit for throwing a pebble at me

 Wow, I thought my wizard was a wimp.

Not mine, one of my players.

Gnome wizard knocks on a giant metal door. Roll to knock. Natural 20. (please don't ask why they were rolling to knock, it's too long of a story. they wanted to) He knocked on the door so hard, that the hinges broke off, and the giant door, at least 40 ft tall and 5 ft thick steel, and they fell on top of the wizard. Wizard is crushed to death as he fails to dodge or duck in time. The wizard lays dying underneath the door as the friendly beholder inside tries to lift the door with the telekinesis eye ray and the party's help.

The wizard rolls his first death saving throw. Natural 1.

The party starts lifting the giant metal door.

Next round, roll for death saving throw. Natural 1.

The wizard dies. He later is resurrected with a major concussion. 

Had a Ronin with an eye patch once that died alot and kept being revived by the party. But Everytime he came back his con score got reduced and he would cough blood. Eventually after a big fight with a lych he died from choking on his own blood.