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1 definition by Ribaldo Givera

 
1.
N. (grAH-vee rayn-bO)

The fecal mustache that is created when a person performs fellatio on their partner after their partner has pitched during anal sex (Ass-to-Mouth).

Although possible in heterosexual encounters, the term Rainbow indicates that it is primarily a homosexual term.
Girl, you've got to get an enema before I poke your keister... you've got a Gravy Rainbow.
by Ribaldo Givera July 25, 2011