"Knock, knock." "Who's there?" "Boo." "Boo who?" "Don't cry in front of me, or else I'll cry!"
Boo Who
Explanation
Explain Bear
Alright, listen up, genius. It's a knock-knock joke, see? The setup is "Boo who?" which sounds like "Boohoo," which is the sound someone makes when they cry. And you cry a lot, don't you?