Those who denigrate out of spite only reflect on their own character, as well as the cowards who may cheer them on. Best to realize that you are above this (you are, you know) and shake the dust of them off your feet. Or, if you feel like having fun, give them more rope to see how much they can outdo themselves as you let them dig deeper into the truth that they are an idiot for all to see. Whatever you do, never continue trying to prove your point once you see clearly that they refuse to dialogue intelligently and insist on attacking. They smell blood and jerk of the year awards ahead when you do that. Never repeat and the truth of what you said will stand stronger in the eyes of those willing to see. :)
You are to valuable to commit to a meaningless battle, always remember your value, my friend.