Las Vegas Handcar
A type of threesome in which there are two females and one male. The male has a strap on strapped to his ass; the women are positioned bent over in front and behind him. The male will thrust both forwards and backwards to penetrate both partners at the same time, thus representing a handcar.
"Hey Dave remember those two girls I took up to my room last right? We did a Las Vegas Handcar! Thank god one of them had a strap on with her!"