Used to make fun of somebody for being dumb. Or worshipping them for having the largest brain and balls of them all. It's yours to decide.
Example one:

Guy #1: e = mc squared.
Guy #2: You've got a monkey head!
Example two:
Guy #1: You're gay.
Guy #2: You're a monkey head.
by Virtual Fella April 26, 2021
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The bit between the Gunt and the Fanny. On a fat bird, the hairy top of the fanny will bulge out like a monkeys head.
Can almost see the Monkeys Head poking out of her trackie.
by Steve 1974 November 10, 2019
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