A sneeky way you can enter your partner, lover, fuck buddy, or whoever, when they are alseep either in the vagina, arsehole, mouth or wherever takes your fancy. Just make sure they don't wake up otherwise you'll just end up looking like a deviant.
Anthony: Hey man, I waited up last night until Karen fell asleep and sleepslammed her good.
Phil: Ah cool, serves her right for not sucking on your balls beforehand.
Anthony: Yeah, lucky she didn't wake up because I had my nuts in her arse.
by Anthony Rees September 14, 2007
Get the Sleepslam mug.