My favorite was when I went to this random Mexican bar in San Francisco. I had to pee really bad, and had just gotten off the Mission and 24th BART (subway) stop. My friends hadn't shown up, so I go to the bar nearby. When I say Mexican, I mean we're one stop away from a Mariachi band and Sombreros, and not the Chevy's variety.
Bypassing the crowded dance floor I make my way to the bathroom. It seems like a one man operation: there's a toilet, a sink, a trash can, a urinal, and no dividers. There's also no lock on the door.
So I start going in the urinal when in busts this dude. So I'm like... okay, cool, finishing up when another guy busts in. He's clearly hammered so I'm trying to get off the urinal ASAP. Too late, he starts peeing in the trashcan. One hand planted on the wall, standing on his tip toes since he was a short guy, straight up peeing in the garbage. Then a fourth guy bursts through the door but I'm off the urinal before he takes the sink...