I have this friend who used to yell out "Whites only" at really funny times while in certain establishments. Part of the reason she found it funny was because of the ridiculousness of the notion. When viewed from this perspective, it really amounts to a denigration of the people who used to (still do sometimes!!) think that way. It was funny because it is shocking and stupid, and it sounds that way.
But, I think that can only be true in communities where racism seems like a long ago memory.