Priming is a school or summer camp prank. It consists of numerous individuals in voice-changer Optimus prime toy helmets(hence the name), (balaclavas and ski masks are used when there are not enough helmets available) and boxers entering a cabin in the middle of the night, turning the lights on, spraying the inhabitants and cranking the cabin heat to the maximum while reciting lines from Transformers, the Michael Bay movie. This is usually a filmed event.
Hey man, have you heard? Our neighbours went priming at 3am last night, and now everyone is soaked wet.