I have a carpark pee story too! :)
I decided one night that on the way back from my friends I was going to take a naughty piss and so I was looking for a place I could relieve myself. I pulled in to a 24 hour parking complex for some shops, which was long closed, apart from the bar next to it and parked up. I had made myself quite desperate by having a cider before leaving my friends and a coffee too! I ran to the stairwell that led to the shops and bar, I went to the top, dropped my skinny jeans and knickers, squatted, and pissed!
My stream started spraying off over the side of the stair