Knock Knockers

Archie wants to do whatever Carter does, and Carter tells a mean knock knock joke. Yesterday Archie took a turn at the wheel:

Archie: knock knock.

Me: Who’s there?

Archie: Nipple.

Me: Nipple?

Archie: Nipple.

Me: (Making a mental note to follow up on the speech therapist) Nipple?

Archie: Nipple.

Me: (giving up) Nipple who?

Archie: Nipple you don’t have a car do you? (room is full of baffled silence) do you get it?

Me and Carter in unison: No.

Archie: (puzzled) What, are they supposed to rhyme or something?