Someone who tries to hide the fact that they are racist. This is often done by concealing their true thoughts by opposite behavioral patterns in the same overcompensating fashion as many closet homosexuals
David: I just read an alarming paper on the socioeconomic position of African Americans.
Jim: Mmm, what? Afro Americans? Sounds a bit racist to me..
David: No it isn’t, listen: analysis of several US federal statistical databases showed that African Americans are more likely to end up in prison than to end up in college. Just an alarming statistical fact.
Jim: You can’t say that! That’s racist man!
David: I think you're a closet racist.