An individual who enjoys disrupting peace of an online message board, and causing dissent in general. They will often claim to possess a skill, called trolling, and speak of it as if it is a useful skill. These people are most likely unintelligent, or not under the realization that there supposed skill is not a skill at all. That is not the only type of troll, other trolls will troll people who are largely disliked, or at least disliked by that particular troll.
Troll: I went to troll some random forum today, I made so many people mad. Trolling is an art, it takes skill to be successful, I am quite skilled in it and take pride in my skill.
Person: Trolling isn't a skill, all you do is make people mad for no reason and you're happy about it when people hate you. You're a waste of space.
Troll: You mad?
Person: You're pathetic.