Oklahoma stampede
When a guy is taking a leak, standing at the urinal, you come into the bathroom and abruptly push his body fully forward. The goal here is for him to come away full of his own urine from making contact inside the urinal. There's not much he can do, assuming he's holding his junk.
Steve just went to the bathroom again. I'm going in there to give him the old "Oklahoma Stampede". Watch my drink.