What is the most subtle form of racism?

People often say, “I’m not racist.” Yet people of other races might still think they are. Racism seems to be in the eye of the beholder.

What is your standard for racism? Sometimes people ask, “Do you have any friends of the other race?” This standard suggests that if you have no friends, you’re racist.

Can a presumption of racism be based just on a look? Is a statement like “I don’t trust [race name]s” grounds to label the person a racist? Is living in a single-race neighborhood racism? Is believing that Obama is a foreigner racism?

What, in your opinion, is the most subtle form of racism.