I've come across a few and got tangled in the mess because they usually bring out the protective person in me. Unless they violate a guideline there isn't much we can do. You can report the post if they've said something and you can voice your concerns to the moderator of that forum. Some say "don't feed the trolls" because they thrive on reactions and attention - I know that's easier said than done. Take it from me, "fellow troll slayer" lol. Had to bring some humor with that one.