Me: Knock knock.
Some dude on the street: Who's there?
Me: Whowhowho.
Dude: Whowhowho who?
Whowhowhowhowhowhowhowhowhowhowhowhowho.
Whowhowho
Explanation
Explain Bear
Listen up, buttercup. This joke is playing on the classic "knock knock" format. The setup leads you to expect a name or a phrase. But instead, you get a bunch of "who" sounds. It's funny because it's so stupid and unexpected, kinda like your last brain fart.