Stop responding to the person who deserves abuse in your view.

Funnily enough, I have! As have a number of others. It does not stop them warranting abuse but, as they seem to thrive on attention, it does seem to have slowed them down a little as well. Sadly they are still getting attention from others. I must say I derive a, possibly perverse, satisfaction from watching them trying and failing to goad people into responding:-)