2. when you hear the sound of someone else jacking off in the room
3. Something utterly horrible.
2. Dude, I was masterbating last night when I heard an offbeat fap, I turned around and my brother was right behind me fapping away.
3. John: Dude check out this picture of this hermaphrodite.
Mike: OHHH dude, that's such an offbeat fap.