Knock knock. Who's there? An anticlimax.

An anticlimax who? Exactly.

Knock knock. Who's there? The premise.

The premise who? The premise for a knock-knock joke needs two people, and I'm talking to myself.

Knock knock. Who's there? Grape.

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

Knock knock. Who's there? Canoe.

Canoe who? Canoe let me in, it's freezing out here!