To get this out of the way, I don't take control of any player character.

Now, my players had a situation where they initiated combat against a group of blackmailers who needed to get away without a fight and one of them was a spellcaster who knew Suggestion and Charm Person. The Charm Person spell was successful on one of the five and told the player that basically she was a dear friend to the player and it would not be acceptable to see your party attack her while the condition is active. That's it. The player had free agency to do what they wanted with that information while adhered to the charmed condition. They started to be pretty upset that they "lost player agency"  and just ended turns doing nothing and sulked after the game saying they don't want that condition again. I don't understand how I can make this situation any better without avoiding the condition entirely, which doesn't seem particularly fair for those who use the spell in the party. 

I'd personally throw charm over stun any day to a player and at least give them a chance to do something. They seemed genuinely unwilling to alter this characters head space. Help with this?

The player is not allowed to exempt himself from in-game conditions. Saying "I don't want that condition again" is saying "I want to be invulnerable to the spell forever." 

I would explain to the player that Charm Person works the way you described, and that this is a valid spell that both PCs and NPCs can cast. If players can do it, their enemies can do it. The only way to make it so that the PC cannot be charmed, would be to take the Charmed condition completely out of the game for everyone, not just for this PC. As that would completely break huge swathes of D&D, because the game designers balanced the game assuming both PCs and NPCs had the ability to Charm one another, the player is basically asking not to play D&D.

So, my position on this would not be unkind but would be firm: D&D has a plethora of character and monster abilities that invoke the Charmed condition when a save is failed. That all characters MUST be capable of being Charmed, and that his character is not allowed to be special in this regard. I would explain that there are some magical items that will protect vs. charmed condition, so maybe the PC should make it his or her goal to seek out such an item. Maybe even make it part of some quest down the line. But not at 1st level! And the PC will have to negotiate with the rest of the party as to why they and not another PC should get the amulet or whatever it is that protects vs. Charm.

But on a larger scale the player needs to learn how to play RPGs. I'm not trying to be condescending here, but having bad things (tm) happen to your character is a part of RPGs and you cannot get angry when this occurs. And almost all RPGs (all the ones I can think of anyway) have something equivalent to the Charmed condition. In Champions, there is Mind Control (also Mental Illusions). In City of Heroes there is literally a Charmed condition. There is a Charm spell in Divinity Original Sin (1 and 2, both, I believe). Rolemaster. Savage Worlds. Ironsworn (with the Compel move). Every RPG has some sort of power or ability that a PC or NPC can use to "mind control" another character. It's the player's task when this happens to RP it properly, not to gripe that their "agency" was taken. No, agency was not lost -- the player is RPing out an effect happening to the character.

If we allow players to argue that the Charmed effect takes away player agency, well what about other effects? Paralyzed -- DM tells you that you can't move or act. Isn't that "taking away agency?" Unconscious condition - can't move, act, react, etc. Isn't that "taking away agency?" Fear. Blinded. Stunned. Grappled, Restrained. Almost any condition you can name is "taking away agency" - conditions limit what the player is allowed to do and may force them to do certain things. What's next? Death saving throws? I mean after all, saying to a player "Your character is dead and you can't play him anymore" is the ultimate in "taking away agency" isn't it? 

But all those things are part of D&D. Fear, Charm, Stun, Paralyze, Death, etc. These things happen to PCs. They are part of the game. Players are not allowed to declare their PCs uniquely immune to some or all of these conditions because they "don't happen to like them."

It'd be like saying in Monopoly that you didn't like the "Go to Jail" card and you won't accept it anymore when it is drawn.

You always have to be careful when a play thinks you're forcing their hand. In all my years of DMing, they'll naturally resist anything that they feel is tampering with their free will. Whether it's reasonable or not. I've had players with years of DMing experience, who understand that you're not trying to rob their agency, still find it hard. 

Charm is one of those edge cases where it can work – but it has to be handled in the right way. The main reason Charm works is because it's not dictating actions, only opinion. From your post, it sounds like you handled it in the right way, but your player felt like you were trying to control them. Perhaps they misinterpreted your intention, or didn't understand the level of agency they still had.

Really make sure you understand the spell yourself (I'm sure you do). It doesn't make the target side with the caster if it's unreasonable. It isn't Suggestion. It simply makes them perceive them as a 'friendly acquaintance.' It might stay your player's hand if they were about to strike in the moment. But if that 'friendly acquaintance' is doing something the player disagrees with, it's reasonable to expect them to question why they think they're friendly, or for the player's party to convince them. Out of game, explain the spell to your player, and maybe offer a few of the scenarios that could have played out if they'd played along.

Provide the barebones information about the effects of the spell, and let the player roleplay it out. e.g. "You suddenly feel as though you know this woman from somewhere, but you can't place your finger on it. She reminds you of your favourite barmaid from your home village... or Erik the baker who always gave you a sweet-roll when you made the rounds". It can lead to lovely RP moments.

But ultimately your player might simply not enjoy RPing out of their comfort-zone. And while being charmed by an enemy, and having your party have to try and convince you that you're not thinking straight, while you protest that they're a friend from... somewhere....sounds like loads of fun, it does require a bit of maturity to get on board with.

I think if you had a chat with your player out of game about what their issue was, and you explained that they still had loads of agency to act as they saw fit, they'd probably be more open to it. This sounds like a case of the player thinking they were under some kind of mind control, and had lost agency over their character,

I agree with biowizard. Even just the first paragraph sums it up. The player can’t decide they don’t want to take damage from a magic missile or they want to be able see the hidden doors. Sometimes things don’t go your way.

The sulking is a whole other thing. Maybe they were having a bad day or something, but watch that. No one will enjoy playing with someone that childish. 

Honestly, charm and suggestion are conditions I'm wary of using, a lot of players have issues with it.

Being charmed is a GREAT opportunity for role-play.

The player gets to play their character differently, and interact with the other party members with a different attitude to what they had just ONE MOMENT ago.

Quote from Farling >>

Being charmed is a GREAT opportunity for role-play.

The player gets to play their character differently, and interact with the other party members with a different attitude to what they had just ONE MOMENT ago.

For this reason, My party's barbarian actually LOVED being charmed lol
Got to do some new RP afterwards, and got to smack the everloving crap out of party members.

Thank you for the replies. It's a little reassuring to know at least I had some of my opinions reinforced in this matter. I tried to explain it to them a few different ways that they would still be able to RP it several different ways if they wanted and they wouldn't accept. The player is one in the group that has played RPGs the longest and I simply don't understand the mentality.

Personally, I've had my INT of a Wizard I play get reduced to 1 and it was a hilarious RP experience.

I agree with the rest that it is not taking away player agency any more than unconscious or restrained.

However, I will also remind everyone that charmed is not controlled. A player at my table charmed a grumpy, loner woodsman whose cabin the party were sheltering in from a storm. She then asked the woodsman to cook the breakfast that she had volunteered to cook, expecting him to fall in line. However, he responded as he would to anyone he was friendly with: "Do it yourself!"

(They also then had to leave fairly quickly, as the spell ended after an hour and he would not have been happy to learn she'd tried to charm him lol)

From the spell, I refer to the part that says "friendly acquaintance".  I know it is not the point of the problem

The charmed creature regards you as a friendly acquaintance. When the spell ends, the creature knows it was charmed by you.

So what is a friendly acquaintance.  Someone you wave to when you see them once a week drive by your house as you get the mail.  Someone you would listen to and follow their directions, like hey come mow my lawn for me.  

Quote from Pantagruel666 >>

Honestly, charm and suggestion are conditions I'm wary of using, a lot of players have issues with it.

I understand it, however... if the players have an issue with  having it done TO them, those same players need to be told that they can't use it on NPCs. It's not fair that the PCs are able to charm and mind control NPCs, but not the reverse.

I firmly hold with the "good for the goose, good for the gander" principle. When one of my players complained about my RAW interpretation of Counterspell, which is that since XGE states that it takes a reaction to simply ID a spell in combat, and you can't take a 2nd reaction on the same round, his Sorcerer would not be able to both ID and Counter a spell at the same time -- thus, Counterspell must be performed blind. We debated about this for a while, and I proposed the rule (yours perhaps, Panta) that if you react to ID a spell you may make a Counterspell as part of the same reaction. He was all for this -- however, I warned him, "If you can do it so can the enemy." 

He had no problem with this... but my point is, if you can do it they can do it.

So... if the players are going to say they don't want the DM to charm or suggest them, then as a DM I'd say, "OK then those spells are banned for PCs as well."

I always tell my players that anything they can do, be prepared to have it done to them. They want that Lucky feat? They better be prepared to find an adversary that has it. I would like to think charm is the same. 

Wow, I guess I take for granted how great the group is I play with, as DM and player.  My son and I take turns as DM and the rest of the group play, but we have ALL sorts of sketchy stuff occur to our characters and we all laugh like fools as it plays out.  Our Charmed Paladin was convinced attacking the Vampire was a horrible idea and went so far as to move between us, which allowed the vampire, (whom he was DROOLING to kill on the way in) to escape.  Post session, he told us he had to stop and think, of how his character would feel if a friend, not a CLOSE friend, but a friend, nonetheless, was the target of the party's anger.  He then had to set aside the hatred for the Vampire and behave accordingly.  It was great fun for all.

I'd push the fun side of things like that on him/her and as DM, make sure it isn't a fatal occurrence of the spell, but something that can be funny.  Maybe come up with a similar situation, but target a different player, who might RP it with a little pizzazz and get some laughs.  Sometimes I find the "OMG!" moments can be twisted into memorable laugh fests.  The Charmed character is told the NPC would NEVER lie to their good friend.  A really simple setup and can be over something truly insignificant.  Kind of a "Wanna see how Charmed can be fun?  Hold my beer."

he told us he had to stop and think, of how his character would feel if a friend, not a CLOSE friend, but a friend, nonetheless, was the target of the party's anger.  

Right -- that is called roleplaying. It is what the whole game is about. It is not "removal of player agency."

Quote from BioWizard >>

he told us he had to stop and think, of how his character would feel if a friend, not a CLOSE friend, but a friend, nonetheless, was the target of the party's anger.  

Right -- that is called roleplaying. It is what the whole game is about. It is not "removal of player agency."

 Can’t recommend this line of thinking enough.  Player Agency is not the issue here at all, and a distraction from something else likely.  Maybe they don’t understand RPGs?  Maybe there’s anxiety tied to some other notion?  You can ask for more info if you want but the “player agency” complaint is just a symptom. 

First of all, if it's not fun, don't do it. Not fair if one player is immune to Charmed but others are susceptible? Fine. Just don't use monsters that can cast Charm Person. Or if other players are okay with the unfairness, just target them.

A compromise that might work is that you don't ever say, "Your character must do this." But you can say, "Your character may not do this." So in this case, the character is under no obligation to defend the caster against the rest of the party. But she cannot attack the caster herself.

And that's within a reasonable interpretation of "friendly acquaintance". I'm going to be at least conflicted about murdering you. I might speak up in your defense. But I'm not going to take a bullet for you.

"she was a dear friend to the player and it would not be acceptable to see your party attack her while the condition is active" is not saying "you must do this" nor even "you may not do this." It is a description of how the spell would affect the character. How the player interprets this is up to them -- interposing in between party and target. Persuading verbally. Etc.

Also, the problem with "If it's not fun, don't do it" -- yes, the game is meant to be fun. That is the point. But if a player says, "It is not fun for me if my character takes any damage in combat" -- how does one have a normal, which is to say typical, D&D experience under those conditions? If the player says, "It is not fun for me if my character ever misses an attack roll in combat" -- again, same problem.

"I don't ever want to have a charm spell cast upon me" is not something I would consider acceptable as a DM. I would have to respectfully ask if someone else is willing to take over as DM under these conditions, and I would probably bow out as a player as well, because I would not be willing to play in a game that has one PC immune to spells the other PCs are vulnerable to just because the player is being, let's face it, a prima donna... and I would also not be willing to play a game of D&D that does not have charm spells, because that is not D&D.

FYI, this is outside of the discussion at hand but there's a decent amount of subtle sexism at play in this thread. Multiple people have referred to the player as a "she" despite OP using male pronouns to refer to them initially, in a way that I feel shows off some uncomfortable assumptions one might make about a problem player at the table.

I think everyone's overall points are valid, just wanted to point out that the way we use language can be a bit uninviting to certain demographics. Please be conscious about it, for everyone's benefit.

The villain is a she, and the player is a he, and the PC's pronoun is indeterminate, as written in the OP.

But the way it is written, if you are reading quickly you might think the player is a he but his character is a she. I did, at first, until I re-read the 2nd paragraph.