A troll is someone who will state something only with the intention of stirring up controversy. Typically the statement is so absurd that only the most noobish of noobs will get offended and respond.
For example, one might purposefuly spel things wrong or use poor grammar, knowing that this will drive some people crazy, eliciting a response.
A more advanced troll might even spell things wrong in a post criticizing the spelling in someone else’s post, hoping to elicit an angry counter-reaction. Numerous forums and Usenet boards are dedicated to the fine art of what the NYTimes called “manipulating other people’s emotional equilibrium” [trying to remember for sure if they should get the credit]
Trolling can be considered a form of cyberbullying and in video game circles the practice is often called “griefing”.http://knowyourmeme.com/memes/trolling
Remeber: Knowing is half the battle.
And that's one to grow on!