1. Seeing as fap is the sound made when masterbating, and offbeat fap is a "fap" sound that is offbeat, suggesting someone else is masterbating as well.
2. when you hear the sound of someone else jacking off in the room
3. Something utterly horrible.
1. fap....fap....fap..FAPFAP....... WHAT THE FUCK WAS THAT?!
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.