A sexual act as defined: Hide in the shower and quietly masturbate while your significant other is taking a dump. Just before you ejaculate, rip open the shower curtain, push her off the toilet onto the floor and blow a load all over her freshly laid poop. Quickly exit the bathroom before being punished.
Person 1: You'll never believe what I did last night! I pulled off the infamous "German Sharpshooter"!