The simple act of intercourse. A great code word that can be used in front of parents, children, and old people or in public places.
Hey dude, what are you and your girlfriend going to do this weekend?
Well I think we're going to see and movie and then we're gonna play some patty cake afterwards.
Tim: What are Jimmy's parents doing after the party?
Jason:They're probably going back to their house for a little patty cake.
Jimmy: What? That's disgusting you asshole.