What did one wall say to the other wall?

Behind the Groan

The Only Place the Walls Can Meet

Two walls in the same room usually join at a corner, so the punchline is a perfectly practical meeting plan. The joke also gives ordinary building parts human schedules and conversations. Ask the setup as though one wall might have something important to say. Pause before the answer, then deliver “meet you at the corner” like a casual appointment. The familiar phrase sounds social first, while the room's geometry supplies the literal picture.