Troll

Troll 

Refers to someone (who is usually cowardly anonymous) who deliberately and often repeatedly makes inflammatory or off-topic comments in a ploy to rile up other people and create dissension. Trolls set out to induce emotional responses, preferably as explosive as possible, and don't actually seem to care about whatever point they are making so long as it starts an argument. In truth, trolls cannot and should not be argued with at all because you can't make them see reason and you are only encouraging them to be even more disruptive if you try. Hence, the frequently used reminder of "Please Do Not Feed The Trolls", because often the only way to get rid of them is to simply ignore them.