I'm not sure, Ben. There's something to be said for ignoring people like that - the best being that it probably would annoy the hell out of them (I find stuff like this is usually done to get attention. Screw 'em. They ain't getting it from me.).
But in this case, the person in question is accusing people of being racist. I'm not sure who's telling the truth in all of this, but if the person is also making pokes at another's disability, as it has been said, that is just unforgiveable. I have epiliepsy; a co-worker made fun of it a few years ago. Man, that *hurt*. It still does. I'm not sure if I wouldn't step up and say something under those circumstances.