hungry brain 

An act, usually public, in which a man hangs his scrotum out of the fly of his pants, pulls the skin tight around one testicle with his hand, and squeezes rhythmically, resulting in a veiny, throbbing effect reminiscent of a 1950s science-fiction monster.

Usually considered vulgar.

They're still talking about the time he walked into Denny's and flashed the hungry brain.

hungry brain by Uncle Leon November 10, 2008