What is Mary Sue? Mary Sue is the character in fanfic that the author inserts for self-justification- self-gratification. Mary Sue is the female who's descended from a unicorn who goes to Hogwarts and who is mysteriously fascinating to every professor. Mary Sue is the werewolf kinfolk who is a mage's consor and who's got a vampire in love with her, in WoD fanfiction. Mary Sue's the woman who turns up in Queer as Folk fanfic who's hot enough she turns every one of the guys' heads.
She's about making yourself feel better- more important. If Mary Sue's world is so great, you can sit and dream about it when you're doing your tiresome data entry job, or your annoying retail clerking, or... all that stuff you have to stagger through to make ends meet that you hate doing.
There's nothing wrong with wanting to have a character who's so perfectly fulfilled in her life (or his: the male characters are called 'Gary Stu's). There's nothing wrong with building a fantasy where everything works the way you want it.
So what's wrong with Mary Sue in an online RPG?
She's just fine to imagine. You're the ultrapowerful sole childe of a vampire a thousand years old. Every man wants you. It's a powerful feeling, imagining such a storyworld for yourself.
The trick is that it's always for yourself. Everyone else isn't in your storyworld. You're imagining yourself as, oh, let's just take somebody from fiction-- Anita Blake.
Who the fuck wants to RP with Anita Blake? The whole world revolves around her- not around her and her friends, not around the group of people she's involved with. The narrative's all about Anita, it's not about the Guy she's Screwing Lately, ever. He only exists in relationship to her.
Can you see how that would suck to RP, as Anita's beloved? Sure, Anita's player would be having a ball- but there's no thought given by the narrator- and presumably by the storyworld's shape- to the other actors in the little drama.
So people who have to deal with Mary Sue RPG get really bored, really quick, and start to either flake off from dealing with her- or start bringing IC consequences to bear. Meanwhile, Mary Sue's reaction to these consequences is that nobody but herself has the right to demand anything in the world. The headmaster at Hogwarts starts saying that Nadine Crossburton is taking entirely too much on her own shoulders as the Astronomy professor, telling students what is and isn't right, and so on- while Nadine's player is sure that she's the center of the universe, and should be allowed to do whatever she damn well pleases because she knows she's right because Nadine's always right because that's how she was made and that's what's supposed to be--
And eventually, Nadine winds up RPing with herself.
What can you do, then? First thing you should do is: accept that you might have gone too far already. It's possible that you've already burned so many bridges with your other RPers that it's going to take a ton of work- perhaps even more work than you're willing to do- to rebuild them.
If you are going to give it a try, then here's a few things I've done for myself when I've found myself going too far down this path and still had time to pull myself out of it.
* Pick a person to consider as the primary character in your world. This can be your IC spouse. This can be a friend IC. act like you're the secondary character in that person's world. You're a standard-bearer when that person's on-stage: you aren't the central character.
* Build a plotline that features someone else. This is much like the prior suggestion- however, in this instance, you build a scenario in which RP might unfold around someone else.
* Ask. If you think you might be being too self-serving- or if you think people are thinking it- just ask. Try to ask gently- try to ask in a constructive manner. You're trying to build RP together with this- not find the traitor.
There may be more on this as time goes on. If you've got a comment on it, please feel free to give it in comments.