When you need to piss really badly you start moving your legs and it looks like you are rapidly humping the air.
Person 1: You ok there mate?
Person 2: No I'm bursting for a piss.
Person 1: Stop Piss Humping. You're humiliating.
Person 2: No I'm bursting for a piss.
Person 1: Stop Piss Humping. You're humiliating.
by StephenHawking'sSearchHistory May 23, 2020
by Jamie Mosshart August 24, 2010