--metagame i.e. use knowledge gained OOC (Out of Character) in game that their character wouldn't know otherwise.
--powergame i.e. overstep the boundaries when doing a scene with another character, forcing them to do actions that they may not want to do.
ex. in a battle, a character is unable to dodge a punch because the other character has declared that their punch has already connected and knocked the first character on their ass.
--twink i.e. develop new abilities for their characters to get them out of tight spots.
ex. a character is trapped and is about to be killed by a monster when suddenly, they develop amazing martial arts skills...that they never had before.
--act out of character i.e. present their character one way in their application and biography but play them radically differently in the game itself.
--engage in pissing contests. Nothing is more boring than to read about two characters trying to prove who is the more powerful/better fighter/etc unless they're willing to make it an actual plot point/rivalry.
--try to get out of the consequences for their character's actions or believe that their characters are above reproach. Consequences must be dealt with, not avoided, for the best interest of the game.
--don't interact with other players (note: I do find it highly amusing when those people then complain about how little RP they get.)
--conversely, pester other players for RP too much. (What constitutes 'too much'? Asking another player for a scene literally everytime they sign on would be 'too much.' YMMV, of course, but if a player complains, it will be dealt with.)
--attention-whore i.e. expect to be the center of attention and will do anything to get it if the spotlight happens to fall on another character.
--retcon (retroactive continuity) i.e. change their character's previous actions in order to get a more favorable outcome. Once the action is completed in scene, it will not be changed, and the character must then face the results of their actions. (note: Some retcon is permissible in the face of glaring errors.)
--expect other players/characters to share assumptions. Do not assume that everyone will believe as you do.
--rape thesauruses. With very few exceptions, purple prose is bad. And somewhere, there is a thesaurus laying in a gutter, broken, bleeding, and too afraid to file charges. Please. Think of the thesauruses.
--believe that their authority overrides that of the GM. The GM is in charge of the game. Unless the GM is irrational and is making mistakes, there is no reason to rebel against their authority.
--pressure other players into storylines. If a player does not agree to do so, they may not be pressured and annoyed into doing so by the other player.