to
make a move on a someone who is very sleepy or was asleep, before you woke him/her up to make a
sexual advance. Jape is generally
successful because when sleepy, the japee is less inhibited and more likely to indulge in instinctive sexual desires.
esp. when the japer is at first with the japee in a non predatory (platonic) way. The more adorable and harmless the japer is, the greater the degree of jape.