Sack is derived from the term "sack of shit". It describes someone who is unworthy of even being filled the feces that would reside within a "sack of shit". It is usually used to describe a person who is extremely lazy or is performing an extremely lazy act.
Friend #1: "Hey man can you shut the lights off?"

Friend #2: "Sorry bro. Busy."

Friend #1: "Dude you're right next to them. Just reach over and shut them off."

Friend #2: "Man that's too far away. I'm busy."

Friend #1: "Busy doing what? You've been playing League of Legends and eating toaster waffles on my couch for six hours."

Friend #2: "Exactly. I'm busy."

Friend #1: "You're a fucking sack."
by Kflop Fats January 25, 2013
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It's when a girl deepthroats ALL the way and her lips touch the scrotum(ballsack)
Ingrid: "Did you get head from that girl at the party last night"?
Opie: "Yeah".
Ingrid: "How was it"?
Opie: "She went all the way down to the sack"!
by TheSackMan July 08, 2010
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When someone slightly lies, but doesn't exaggerate the truth enough so that it is actually impressive. Most commonly used to increase ones self esteem, but not exaggerating so much that it is unbelievable.
CJ: You seem smart, what math course are you in?
Ian: Calculus AB
* actually in honors calculus *
Jason: First, why would lying about his math course make him look cooler? Second, why wouldn't he just say he was in Calculus BC if he wanted to look impressive?
CJ: I guess he was just sacking
by Bro Code Vocab June 30, 2015
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The male scrotum. Used as an exclamation for emphasis or to show dismay.
Asian: Hey dude you know we have a quiz in physics today?
White Boy: The sack!
by stuuuu October 05, 2006
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