A nigger nap is a way of sleeping while you are at work. It is when you go to the bathroom and sleep while standing in front of the urinal so that it looks like you are taking a piss. Be careful to not fall. Niger naps are not very comfortable or easy to accomplish but one is tired enough, one might be able to pull it off.
Hey James, I'm gonna go take a nigger nap. If the boss asks where I am, tell him I went to take a piss.