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The distance between two cocks during dual penetration sex. Measured in millimeters.
Hey Earl, thanks for fucking my wife with me last night.... I bet there was only 5mm Betweenis.....
by MotoRooster September 28, 2007
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The choice at the end of the night between which weenis to use for a booty call.
Chessa was torn betweenis for JG or AP.
by Maxurethra March 25, 2010
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