Comic Genius

Mommy: Knock Knock

Marty: Who's there?

Mommy: Boo

Marty: Boo who?

Mommy: Oh, don't cry Marty!

Marty: HAHAHAHAHA! My turn, Knock Knock

Mommy: Who's there?

Marty: Joe

Mommy (I can't imagine where this is going but I guess I must play along): Joe who?

Marty: Joe mommy! HAHAHAHAHAHA! PopPop taught me that!