one who rubs themselves in their 'special place' while sleeping. The purpetrator is usually completely unaware of his jolly good time in the morning.
rob: *rub*rub*rub* "ZzZzZzZzZz"
jack: hey everyone look, alan is sleeperbating
everyone: jeez, he's getting more action than a 2 dollar whore.
jack: yep. he's a very talented sleeperbater.