I try to point out how pathetic they are being. I try and point out the irrational and uncivilised mentality they have.
In real life I hardly ever get dissed, because I never react in a way in which would be 'expected' rather I exchange a their wrongs with a right. If people have any civility in them then I always know how to make that person feel ashamed, if I come across a fool then I run. Literally I run away from them. but the key is to be cheerful.
To turn around and attack or kill or even reciprocate their dissing with a reaction which is equal or above what was meted out to you is the cause of a lot of destruction of the fabric of society.
Also never be ashamed of being the person who shows the kindness or the quality of being someone who doesn't want conflict. becasue apart from the fact that you are burning bridges, this quality is something which I think is a true wealth