hackey sack
A fake fat butt. It looks big at first, but then you squeeze it, and it’s just a lean ass hiding in a sack.
'I thought his ass was huge, but after I squeezed it, it was just a lean sack.'
'She had a hackey sack-ass, and I knew it was fake the whole time.'
'He had the biggest sack-ass I’ve ever seen, but it was just a trick.'