There are all sorts of generally anti-social behavior that drive me nuts. Players that get super-aggressive and OOC angry over something that other players do IC or when they don't get there way just drive me to distraction. Probably the number one RPG crime is simply "being a jerk". Specifically, when your actions as a player are motivated by anger, envy, pride or selfishness, you are being a jerk, even if you are a high charisma type that can generally disguise your underlying motivation. It's Ok to have a character motivated by such things, but keep your distance.
As for the sort of RPG "crimes" that aren't general social crimes, but specific to an RPG, one of the worst is creating a character that has no motivation for getting along with the rest of the party. It's supposed to be a social game, so make sure you make a character that fits in with the overall dynamics of the existing characters. Don't decide to play a dishonorable pirate if everyone else is honorable paladins, or vica versa. I can see possibilities for that working, but generally it requires consensus, skill and effort on both sides, and most of the time what it takes to make it work just isn't present. Likewise, don't create a lone wolf character, or an anti-social character, or a character no one would really want to have around. Your character needs to be part of a team, and the other players ought to want to have that character on the team. The worst case I've ever seen of this is a player created a character that was phobic of other people and who had lived in isolation, but no backstory at all regarding why they'd want to come out of isolation. Then they (I guess) expected play to revolve around coaxing them to be part of the group? I was never sure what they intended.
Similarly, don't deliberate create a spot light hog that is going to dominate play. Don't create a character that is going to through system mastery be vastly more powerful than the prevailing standard for the group. And remember, the #1 rule of RPGs is, "Thou shalt not be good at everything.", so even if you find a way in the system to break that rule, avoid it unless you are the only player at the table. This rule can and should be construed as going so far as to ban you from playing heavily optimized tier 1 class characters unless everyone is. You can play a tier 1 character, but if you are already playing a tier 1 character, don't also decide to make this the best darn most optimized tier 1 character you can play. Play a Jack of All Trades, just don't play a Master of All Trades.
Don't create a character which, however useful the character is to the group, is going to absolutely dominate how the group interacts with NPCs unless everyone is on board with that. For example, if your character looks like some mutant monster or is actually a vampire or something like that, make sure you can disguise your infirmity from most NPCs so that the group doesn't become the group that all it does is protect your PC from society. Even if your group is OK with that as a table subplot, make sure it isn't the only story being told.
Don't create a character with backstory that in and of itself is more important or as important as the main campaigns backstory, or at the least, don't expect such a character to be approved. If your character concept is "The Chosen One" and turns every other PC into a henchmen that exists to help your PC fulfil your destiny, chances are you are trying to hog too much spot light. Again, I can foresee circumstances where this sort of thing is cool, but make sure everyone is on board with your idea including the GM and the other players, and don't get too upset if the group decides, "Nah. I don't think so."
Someone else has already said it, but cheating also falls in this category. It's a form of spotlight hogging, because your character is always the one that succeeds, always the one that comes up big in the big moments, and so forth. Aside from the spot light hogging, it is also really annoying when I can tell a player cheats - and I definitely can tell. It's not the like a near complete absence of failures and a tendency to consistently beat the odds won't go noticed. Although, cheating also goes up in the general category of "social crimes" where you'd think, "Don't be a jerk." would cover it.
Slow play is also annoying, though the worst cases I've seen weren't in RPGs. Occasionally you run into a player that is so competitive and/or afraid to do the wrong thing, that they undergo decision paralysis. They have to work out everything that they are going to do in the finest details and review every possible option before it comes to a decision. That one is at least curable though.
The opposite extreme, players that never work out in advance what the consequences of their actions might be and are always impulsive are probably worse. Of course, the main problem they cause is an ever revolving cast of characters, since they tend to die at 4-5 times the rate of the PC's of other players.
tl;dr: I guess I can sum up all these specific problems as forgetting that you are supposed to be playing a cooperative social game.
