Does this extend to IRL tabletop roleplay as well? Regardless, here goes:

The thing that irks me about tabletop, nominally D&D and Pathfinder, is shitty group dynamic. It's 100% more enjoyable playing with friends you know well and can trust not to abuse the game, or disrupt the flow of play. Playing with strangers makes me want to flip the table. I don't have any GM experience, so this is coming from my background as a player. I understand that people play the game for the freedom to be whoever they want and do things they can't in normal life. But that's hardly an excuse for being insufferable pricks. 
I can't stand the murder-hobo mentality, ignoring any sensible norms that the GM's world may have and doing fuck-all to delve into the plot (if there is one). Part of me thinks the casual, pick-up style of official modules and things like Pathfinder Society is to blame, being very combat/encounter-oriented and eschewing roleplay. 
Every group also has that one jackass that thinks he's the next king of standup comedy. I don't mind out-of-character banter when appropriate; it's actually somewhat necessary to break the ice in a group of strangers. But why do people feel the need to insert their shitty one-liners at every opportunity?  
Then you also have your powergamers and outright cheaters, rules-lawyers and so on. The assholes that'll do anything to get a leg up on everybody else in the party and have the 'me vs. the GM' mentality. I have no patience for people who adhere unflinchingly to the rulebooks as written, and refuse to acknowledge discrepancies in the GM's setting and the game's own. 

When I roleplay, I do so for the story. To be someone I can't and to explore a world different from my own. The things that stand between me and fulfillment of that objective is 99% other people. And I hate them for it.