When a man is on another man lap getting anal. The guy on top gets a reach around, and the one on bottom pulls out at the same time they squirt their load.
The act of coitus interruptus followed by urination, i.e. pulling out early, cumming on a female's stomach, then immediately pissing whilst the penis is still erect, such that both fluids form a rainbow-like arc.
After six King Cobras and already breaking seal, I couldn't hold my piss in anymore, so I figured I'd give my girl a double rainbow. She was so happy she cried 'Double rainbow all the way, what does this mean!?!'