A humorous insult not particularly referring to anything with complete certainty. Could be referring to the male genitals or something else completely.
A stretchy skin pouch used to house the testicles. Useful for storing a load until it can be squirted onto a girl's face. Especially if said girl likes the taste of ball sweat.
"hey babe, I heard you like salt and vinegar"
"lol ya it tastes like ball sweat"
"Wanna lick my sack while I jerk off and cum on your face"
"omg really? Will I get a fat load?
"yeah coz you're a dirty skank"
"sweet"
In Iowa this term refers to a plastic bag which you may be offered at your local gas station or grocery store. If anyone ever offers you a sack, the correct response is, "sure, I'll take as many sacks as I can get." A sack can also be used as a pair of shorts in a drunken state.
"Would you like a sack with your busch lights and magnumcondoms?"