Yeah I know it's a double post, but it just came to mind....
People who undermine you winning a match, simply because of your tactics, character, rank, hell even your costume color (I'm serious on that one). If I lose, I learn from it, congratulate the other guy, and move on. Some players forget that it's just a game after all. When I can pay bills or score points with the ladies by playing fighting games, then I'll be a bit more serious. Until then, IT'S JUST A GAME.