Knock knock. Who's there? Wu

Wu who? Wu don't know, I'm having an identity crisis, but I'm paws-itive I'll fur-get about it.

Knock knock. Who's there? Tank.

Tank who? Tank you for opening the door!

Knock knock. Who's there? Maple.

Maple who? Maple syrup to talk to someone, I'm feeling a little drained.

Knock knock. Who's there? Existential Crisis.

Existential Crisis who? I'm not sure, but the meaninglessness of this joke is a reflection of the void that lies at the heart of our existence.