Troll

"An Internet troll, or simply troll in Internet slang, is someone who posts controversial messages in an online community, such as an online discussion forum, with the intention of baiting other users into an emotional response" - Wikipedia definition

Pretty much any internet forum, discussion board, or editable resource is at risk from the troll. Trolls like to provoke a reaction, to get attention, regardless of the type of attention it is. Some trolls try and cause infighting between established members of a site, to split the group apart for their own amusement. Others post quite random, inane comments, to confuse and perplex (see cheesepie).