The act of a man and woman having sex
tied to a chair placed at the top of a staircase, and after climax, tipping themselves down the stairs. Often referred to as "buying" a non-refundable bus ticket.
John: "Hey man, how did you get that scar on your leg?"
Paul: "My girlfriend and I decided to try buying a non-refundable bus ticket."
John: "Ouch, dude."