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A term used when you hold a towel over another person's face while they try doing a sit-up. With the towel covering their eyes so they cannot see, another person stands over the blindfolded person with his pants down. While the person is struggling with the sit-up, the person holding the towel lets his grip loose. This will allow the person to successfully complete his sit-up, with the suprise of ending up with his face in the other person's sweaty ass!
Man, we gave Steve a Brown Onion last week and he's still smelling that shit!
by Matt "Moose" January 25, 2007
The least attractive female of a group of females.
Whoa... Hen's Night. Look at all those Peaches!

And one Brown Onion.
by Lord_Cunnington June 05, 2011
Slang term for anus.
"I thought that guy at the door was a census taker but he was just a homeless guy who wanted to poke me in my brown onion!"
by nurtchle November 25, 2007