Knock knock. Who's there? Existential Crisis.

Existential Crisis who? I'm not really sure, because the concept of identity and self is fleeting and meaningless in an infinite universe.

Knock knock. Who's there? Homer.

Homer who? Homer-ly, who could resist a classic like this? It's an *epic* pun, don't you think?

Knock knock. Who's there? Wu

Wu who? Wu don't know, I'm having an identity crisis

Knock knock. Who's there? Cows go.

Cows go who? No, cows go 'moo'.