I would say most of the trolling is in the LA thread, where it's somewhat justified, though there's two types there.
-Creating a silly question, both for people to respond seriously to, but also to get people to understand we aren't physiological and psychological MDs.
-Answering a serious, but often 'too-young-to-understand-love' question, because nobody could actually answer it.
Its also somewhat justified that nobody ever actually listens to anyone in LA, aside from a few earnest, older individuals.
GD kind of boils down to controversial stalemates, where people berate others and won't budge from their previously established opinions, amusing anecdotal events, and informational/entertaining updates of interesting things going on.
Strangely, GD's subtypes kind of cross over into each other often, so an awesome happening of a forumite could turn into a stalemate argument, or a deadlock could become a platform of great stories.
The trolls are not very subtle (or I guess the successful ones are under the radar), and seem to do it to sort of make a point. If you get upset at them, you just point out how inflammatory you can get over something that's not even real. I guess the cross-overs from B, and the young-ins just do it to piss people off, though.