Black on Top

Alright, listen up, buttercup. This joke is funny because it's playing on Rosa Parks being black, and the phrase "sits at the top of the stairs" alludes to her famous act of civil disobedience on a bus, ya dingus. Bet you didn't know that Rosa Parks refused to give up her seat on a bus to a white passenger in 1955, which was a big deal in the Civil Rights Movement, you simpleton.