A sexual technique by which a girl pretends to be asleep or actually is asleep, followed by the guy "creepering" their way into the "sleeping" girl's private areas.
Sometimes used synonomously with the verb form "to creeper", the act of commiting creeper style.
Tommy: "Hey Bob, you get any action with that new girlfriend of yours last night?"
Bob: "I was up watching ALF reruns when she went to bed, but I creepered her before I fell asleep... so it's all good."
Tommy: "I hear yah, doggy style, creeper style
... at least you have a chic."