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1. Devil's Threesome
A threesome including one woman and two men.
"Jane really got a good workout when Dick and Tom gave her Devil's Threesome"
2. Devil's Threesome
A ménage à trois in which the ratio of guys to girls partaking in the sexual experience is 2:1. It is the worst ratio to have in a threesome, except of course 3:0.
Tara: "So last night I had a ménage à trois"
Sara: "What's a ménage à trois"
Tara: "A threesome."
Sara: "OH!!"
Steve: "Was it two girls and a guy, or was it a Devil's Threesome?"
3. Devil's Threesome
A threesome that involves two men and one woman. Balls get entangled, completely the wrong 2:1 ratio of a threesome.
As Barney Stinson puts it, "Thou shall not make eye contact during a Devil's Threesome."

It's Bro Code.
4. Devil's Threesome
-phrase
1. A threesome involving two "horns"
2. A sexual encounter where a woman has to deal with two cocks at the same time
3. A sin against God (even if you don't believe in him)

Origin:
Some sad fuckers who wanted to claim they had a threesome.
A "Dude, I had a threesome last night."
B "Awesome, who with?"
A "Cindy and Joe"
B "Who's Jo? Is she fit?"
A "No, Joe is a guy"
B "........"
A "Joe is Cindy's ex-boyfriend - it was a Devil's Threesome"
B "Get the fuck away from me, loser."