Troll: In Internet slang, a troll is a person who posts inflammatory, insincere, digressive,[1] extraneous, or off-topic messages in an online community (such as social media, a newsgroup, forum, chat room, online video game, or blog), with the intent of provoking readers into displaying emotional responses,[2] or manipulating others' perception. This is typically for the troll's amusement, or to achieve a specific result such as disrupting a rival's online activities or manipulating a political process. Even so, Internet trolling can also be defined as purposefully causing confusion or harm to other users online, for no reason at all.
Using that definition, most of us have probably been at least trollish at some point.