Ying Yang Bang
When two people are performing a 69 on each other while two men are fucking them in the ass.
Guy 1: "That was a wild sex party I went to last night. I saw two people 69ing each other and there were two dudes fucking them in the ass while they did it!"
Guy 2: "Damn you saw a ying yang bang!"
Guy 2: "Damn you saw a ying yang bang!"