Knock knock. Who's there? Alpaca.

Alpaca who? Alpaca the suitcase, you load the car!

Knock knock. Who's there? It's me, Kevin. We talked about this. I'm here for the pizza.

It's me, Kevin. We talked about this. I'm here for the pizza who? Seriously, it's just Kevin. You ordered a pepperoni, right?

Knock knock. Who's there? Fig.

Fig who? Fig-ure it out yourself!

Knock knock. Who's there? A small grammatical error.

A small grammatical error who? You should have said 'Whom's there?'