I had a situation on the Bladeforums where someone was very rude and I thought way out of bounds. I said that I was leaving and was surprised at the persons behavior, thanked everyone and left. That person was later banned, returned, banned again, returned, banned, returned, banned....17 times.
I did'nt think I needed to say anything about the person, he made his own arguement. If I say something and I'm challenged on it, I try to present the logic, reason and facts that support my opinion. If that is not sufficient, there is really nothing else for me to say.