Knock knock. Who's there? Who.

Who who? No, YOU'RE asking 'who.' I'm 'Who.'

Knock knock. Who's there? Knock

knock.

Knock knock. Who's there? Ego.

Ego who? Eggoing to let me in, or is that just a waffle excuse?

Knock knock. Who's there? Philosophically speaking, the notion of a 'who' is a social construct and the concept of identity is fluid, so the idea of a fixed entity on the other side of the door is a fallacy.