What is it about a supposedly consequence-free environment that encourages trolls to act like trolls? Maybe it's all that dribbling machismo looking for a smackdown but not finding it. Friends don't let friends troll. If you find that a friend's been trolling, smack them in the face. If your friend keeps trolling, smack them in the face again, this time with a brick.
(Pacifist much? Heh. I think work's been getting to me.)