Joanne has the story of a teacher who--well, just go read her few paragraphs yourself. If you don't want to surf, I'll give you the punch line: “C.H.A.N.G.E. — Come Help A (N-word) Get Elected.” Now go take a look.
I have no idea if the person in question is a racist or was just being provocative for academic reasons. The news story Joanne links to doesn't give enough information from which to draw any such conclusion. I'm pretty sure that most of us can agree, though, that he certainly exercised poor judgement in either case. I'm not one who believes that one example of poor judgement, even in this case, necessarily merits being fired, but if he were expressing racist beliefs, I would. That dichotomy makes me very uncomfortable because I don't like thought police. I need to give this topic more consideration.
Here's an interesting question, though: what is the best reason for excluding racists from teaching?