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A sexual position encountered during a threesome or Menage a Trois. Characterized by one male performing oral sex on a female as she is lies declined (downhill) while she simultaneously performs oral sex on male #2, who is in fact lying on his back on the floor.
1) Yo homie, I heard that Ralph was doing a Downhill Double Dip the other night. He said it was crazy!

2) Did you see that chick when she was Downhill Double Dippin'?! She is very talented.
by Ralph (DMS) Castro June 05, 2010