Bad behavior is cyclic. Its the same way in a school. Kids are great most of the time, but suddenly everything flies to hell at once. The best thing to do is to be consistent, respectful, and a little understanding. (I've had a sneaking suspicion that many of the "trolls" are actually kids.)
About the only thing that one can do before the staff takes action is gently lay out some online behavioral expectations and encourage good behavior...nothing official, just friendly advice. Another thing that one could do is use the reputation system to point out the diamond in the rough. I figure that most people are already handing out red marks, so I'll give a greenie to highlight what is acceptable.