You're racist!

I find the best response to ridiculous charges of racism is to laugh out load, clap my hands a few times, and thank the accuser for publicly admitting s/he has nothing substantive with which to rebut anything I said, and therefor must try to shut down the conversation before anyone notices.

"You're racist!" actually means "I admit that I lose!" Such people should be immediately thanked. It drives them nuts, though, so be prepared to receive a violent assault.

Michelle Malkin has a dictionary of "code words" which really get the accusations going strong.