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2.
A term used to describe the effect on a man's penis when having doggy style intercourse with a woman who wipes from back to front, thus leaving a small amount of feces around the entrance to her vagina.
My friend was fucking Misty from behind, and after he pulled out he noticed he had brown rainbow. Misty is a dirty ho.
by JasonW October 27, 2005
 
1.
taking a dump two feet behind someone's bedroom door then closing it behind you.When the chump opens the door all the way he smears the turd into the carpet in a lovely rainbow design.
they'll be scrubbing that rug for a week before they erase the brown rainbow I left them
by rod fury April 20, 2006
 
3.
a cleveland steamer, but between homosexuals. when a gay person (rainbow) has a bowel movement (brown) on their partner's chest as a sexual fettish.
Larry & Carl were kinky homos, they liked to give each other a brown rainbow once in a while.
by dude98765 May 25, 2011