Hackey sack-ass
It looks like a fat ass at first, but when you squeeze it, it's just a bunch of air and a little bit of meat. Like it's trying to trick you into thinking it's got some real stuff going on.
My cousin tried to grab my hackey sack-ass and got nothing but a laugh from me.
He squeezed my ass and it popped like a balloon. I laughed so hard I cried.
At the party, my friend tried to grab my hackey sack-ass and ended up with a slap.