What do you call a black man on the moon?
An astronaut.
Alright, listen up, genius. The joke plays on expectations. You think the answer will be some kinda stereotype thing, but BAM! It's just "astronaut". It's funny 'cause it's not what you expect, and it makes you, the listener, feel a little silly for even thinking that way in the first place. You probably read Breitbart all day.