When two women lay down, one on top on the other (missionary style). They then push their vaginas together and the male(or for lack of male, third woman with a strap-on) comes in and fucks the spot in between them. This stimulates the clits of both women and the male's penis at the same time and everyone has a great time.
Guy 1: So I heard you banged Susan and Candy at the same time last night, you pimp!
Guy 2: Yeah, I got them both drunk and had myself a clam sandwich.