Silent Assassin
A prank where you wait for someone to go to sleep. Once they are asleep you start to jerk off. Once you are about to cum wake the person up and cum on them. Thus called the "Silent Assassin"
Person 1: "Dude WTF?? Why are you jerking off?"
Person 2: "I'm about to Silent Assassin that bitch in the other room."
Person 1: "OH, HAHAHAHAHA!!!!"