When you first squeeze the ass there is some give, giving the squeezor the illusion of a "Fat-ass." However, upon further squeezing, the squeezor realizes that said ass is rather lean at its core, hence the name hackey sack-ass, due to its resemblance to a hackey sack.
Girl 1: "Ya I thought his ass was fat but upon further squeezing I found it to be rather firm."
Girl 2: "Like a hackey sack?
Girl 1: "Ya Totally, it's a hackey sack-ass!!"
A sack-baggy of drugs stuck up ones ass for conveyance (ex. into a penal facility, through airport or seaport security.)Also done to prevent discovery by police.
WORK RELEASE INMATE 1: "why you so boogered up homie?"
WORK RELEASE INMATE 2: "cause i had this ass sack of blow nigga"
When a faggot has sex without any lube, really jamming it in there, and then pulls out before cumming, therefor causing the inside of the asshole to come out with the penis.