Knock knock. Who's there? Existential Crisis.

Existential Crisis who? I'm not sure, I've been questioning the meaning of my own existence and the nature of identity, so the concept of a 'who' is somewhat fluid to me.

Knock knock. Who's there? Wu

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

Knock knock. Who's there? I'm not sure.

I'm not sure who? I'm not sure who is asking, can you please state your full name and the purpose of your visit?

Knock knock. Who's there? Sew

Sew who? Sew glad you asked, it's a tailor-made joke!