the act of throwing your own ejaculate at someone, most often at their face.
Buttercupping, thats farting on your hand and cupping it over someone's face.
Punking, that's the apotheosis of bodily fluid weaponization.
"Aaaaargh, my eyes!"
"You just got punked, bitch."
2. succesfully playing a practical joke on someone
Originally, the word "punk" was prison slang, meaning the first defintion. the second comes from the idea that fucking someone in the ass is a sign of disrespect (such as male dogs humping one another to show dominance, instead of sexual attraction, which could very well be the motive behind prison rape as well)