The definition of racism is thinking you're superior to another race. That's it. Any race can be racist however not every race can enforce institutionalized racism.
If a black person or race can walk into store A because a white owner refuses to give him service is what?
The black can think he's better than that white person because he wouldn't stoop so low to do such a thing to only serve to a certain race, so is that black person a racist?

