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? Cows go.

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

Knock knock. Who's there? Fig.

Fig who? Fig-ure it out yourself, I'm busy!

Knock knock. Who's there? Grape.

Grape who? Grape to meet you, I've heard a lot about you!