In a venn diagram, each of the men has one girl to himself. The remaining girl is shared amongst the two men, and is represented as the overlapping region of the venn diagram.
Stacey, Jane and Amy: "Sounds like an orgy baby...yeah, count us in."
Amy: "Shotgun being the overlapping region. I love double penetration."
Mark: "Damn. You get her number?"
Jared: "Nah, but she let me slap it a few times while her boyfriend was ordering hot dogs."
Mark: "Sweet. You know, your girlfriend has quite the venn diagram too."