Human pinball machine
The act of three people have sex with a man in the middle using his dick to screw one person while he uses a backwards facing strap on to screw the person behind him. He then moves forward and backwards making a human pinball machine.
Bob: Dude I had a threesome last night
Dave: How'd that work out?
Bob: We did the human pinball machine
Dave: Atta boy!
Dave: How'd that work out?
Bob: We did the human pinball machine
Dave: Atta boy!