I haven't run into them here. I really believe that's a credit to the moderators and the community. It's just not accepted in any way, shape or form. On other forums, I see them often. Sometimes, it is interesting to watch the train wreck. It's disturbing to see less mature and developed online arenas where even the moderators will give in to their baser instincts and join in flame wars and such.
Having said that, I just stay clear of them. I haven't had one post on my info here. When they do elsewhere, I ignore them. Well, I call out the fact that their inability to post constructively is not why the rest of us here, and then I ignore them. I may remove their comments, pending on my permissions. If I ran into here, I might do the same. At the same time, because of the response here, I'd probably just go ahead and flag it as well. My problem is with the spam comments. I have to go through and delete them every so often and flag it, but often the account is already disabled by the time I bother to waste any time or energy on it.