Ah, the notorious troll. Perhaps you've come across one—those people who deliberately try to get under your skin. Sometimes, that means trying to piss you off. In a game, that could mean verbally harassing or annoying you, if not playing specifically to get in the way. That's the most standard conception of a troll, anyway. A troll could also be someone that convinces you of something silly or outrageous. A ‘good' troll manages to enrage or deceive the victim. A good troll also stays in-character no matter what.
I've written about all sorts of trolls in the past. Here is one that adopts a number of grating voices in Call of Duty. Here is one that pulls Xbox Support's leg by claiming to have an issue with an Xbox (and here are more trolls sending Xbox support questions.) Here is a troll that harasses women gamers for, well, being women.