Is it rude to reuse characters in different campaigns?

I've made some characters for campaigns that fell apart early or oneshots, so these characters fell out of use, but I put a lot of work into making them (especially for campaigns that fail) and I really want to play them, so is it bad to reuse a character from a dead campaign in a different campaign?  I would never want to be disrespectful or rude and sometimes I have characters that really just didn't get justice in a campaign cut short, so would that be okay?

It depends on what the group is playing. If the character is thematically appropriate for that campaign, and you have (have had) fun playing them, go ahead. Re-use, re-cycle ;)

Even if you only ever make one character and play them in every game you join, it's not rude, if the character 'fits'.

If you re-use the same character with the same group of players over and over again, it may be rude, if your fellow players get bored of that character, however.

I think it depends. If its a new group with new players, that's fine.

If you made a character which you were really happy with, and they just got instigibbed before having any development, that's fine too.

If they had a decent arc, or it's the same campaign you already used them in, I think that's pretty rude to reuse them for.

Ask your new DM "can I use the characters from my last campaign, I put a lot of work into making them, and I would like to reuse them, do you mind?

I can't think of a reason anyone would object, unless it is the same DM and the character was a murdering hobo that ruined the first campaign.

I agree with 256 and Greg.

As a general rule of thumb, it is generally preferable to create PCs with the specific campaign in mind. But if you have a Character that is appropriate to the new campaign, and you have the DM’s approval, then I see no problem with it.

The DM may ask you to redo your Ability Scores though depending on if they have a preference of which method they want used for their campaign. Like, for example, some DM’s use rolled Ability Scores, and others will only use Point Buy or Standard Array. Other DMs have their own custom Point Buy or Standard Array instead of the ones in the PHB.

I think it's okay if it's with a new group, you are willing to make a new character sheet for the new incarnation and you don't talk about the your adventures with the character from before (either too much or at all with the other players).  I think you would need to do a bit of a reset mentally on your character in order to roleplay them at the level that they are in the current campagn, especally if the characters are starting back at a much lower level than where you were with them in a previious campaign. 

I think you would need to be  honest with the DM about what you are doing (get permission), but it would be okay reuse the name, character concept, backstory, personaliity, race and subclass, if you want, but be flexible about changing (hopefully improvinig the character some, in this interatoin.). I'm actually not sure if it is a good practice to tell the other players that you've played this character before.  Honesty is good, but I think it could take something away from the enjoyment of the other players, espeically if you talk about it a lot (and perhaps not mentioning it is best).  

Now wondering about doing that with people that you've played the character with before, if the character was beloved, there has been a gap in time of a least a couple of years, since you played the charaacter, and they are okay with it.  

I guess there's also the risk of character death and being more emotionally attached to a character, starting out in the campaign.  If a character that you were really attached to,  died early on or in a way that didn't seem befitting, you might wish that you had left them in retirement from adverturing.  

I'm in the "depends" club. Like others, I see no problem bringing in a character (concept) you loved before and trying it in my game, provided it fits the setting, cultures, etc.

I have had friends who want to run the same character every single time because they love the concept. It's only destructive when it doesn't fit. It may be tiresome to go, "Oh yeah, here's John Doe and his Dragonborn Assassin again!" but if John's having a good time and contributing to a healthy and happy game table, I'm good.

In terms of the "reusing" aspect per se, no, there's nothing wrong with that. Especially if it's with different groups. I wanted to try out my Artificer before committing to him in a campaign, and my FLGS was doing a one-shot, so I took him. The first time I went there, I'd taken a character I'd already played a (small) campaign with. Not an issue.

The only issue really is if that character would be problematic regardless of the resuse. If it's built on the wrong theme (eg a comical Spelljammer character for a Curse of Strand adventure might be unwelcome) or there's a mechanical issue (that character you rolled straight 18s with likewise might be a problem) or something else that causes problems at the table.

Notice that the problems aren't really caused by being reused but by problems with the character itself. Reusing a character might cause issues to be more likely (creating a character for Spelljammer is more likely to be inappropriate for Strahd than a character made for Strahd, and you're more likely to reuse a character that rolled straight 18s than one that had more mundane stats), but so long as its level appropriate, then reusing per se isn't really an issue.

Some DMs might get precious about it though, so don't assume.

I don't see it as rude or anything to re-use a character, it is the property of the player afterall. A PC is compromised of two parts, mechanical and story. Nothing prevent you from making the same character for a different campaign, provided all mechanical parts are permitted bt the DM. But storywise, it can be harder to use the same as the player and the DM would have to iron out the kinks, if any, to make it work or fit the campaign. The character experience could be before or after the current campaign etc...

In the end what matter most if to have fun isn't it?

It depends, on if you are in a current campaign or not.  That would be grossly unfair, but only if you kept any new weapons or magical items.  Otherwise. If you guys don't have a game or it is being suspended for whatever reason.  Why not joing a One Shot? 

For me it depends on what level you're starting the campaign as, I let my players use an existing character as they were only level 4 from the last campaign, but if they were a higher level, like level 15 for example I will probably ask them to use a different character as running combat gets harder at higher levels.

hope this helps :p

It depends on the table and campaign/one-shot involved.  If I needed a Forgotten Realms character, it fit the party composition, I had some story that would work it in AND the DM was OK with it, I would happily bring in an old character.

When we played through Shadow of the Dragon Queen, three of our four characters were recycled. One was my elder son’s very first character (a high elf Evoker, made from the 2014 free rules) and two others came from an exceedingly short-lived campaign: a Minotaur barbarian (with a name change) and a character kept only their name and their size (a halfling monk who transmuted during character creation into a Kender paladin). 

The Planescape campaign (Turn of Fortune’s Wheel) uses the idea of characters having different versions of themselves across the multiverse (see also the Spider-Verse films). So, introducing the same character into different campaigns is not that difficult to justify. However, you need to be happy to rework the character with your DM to fit into the new campaign setting. Also, it mustn’t be merely a pretext to port over your straight 18s or that powerful magic item. 

If I'm DMing a full campaign I like everyone to have custom made characters, I build big chunks of my campaigns around their backstories which doesn't work unless the character is part of the world. However for one shots it's a free for all and a lot of my players have their special "one shot" character that they always use and in one case she's even written a back story about her character being trapped in a endless loop of dying and being reborn in new worlds for new adventures 

Characters need to be adjusted to the world that they are playing in, and that is all.
Reusing a chracter is in no means disrespectful. The only way it would be is if the DM had specific new options or restrictions on options and you tried to slip in a character that broke those rules.

I even made a huge setting that never got used that the entire conceit is to use characters that died or were retired, because this is such a problem. Characters made then never used outnumber characters that saw full campaign completion.