Lamb's Brain 

When a man flashes his testicles (and only his testicles), pulled up and taught to simulate a lamb's brain. Usually used for offensive humor after the question "want to see a lamb's brain?" or "have you ever seen a lamb's brain?" The person questioned is usually not given time to respond properly before being flashed.

Peter: "Want to see a lamb's brain?"

Brian: "Wha...?"

Peter: (shows)

Brian: "Ewwwww, nasty!"

Lamb's Brain by TheDoof February 21, 2009