The phrase "nut sack" is a slang term that refers to a part of a male's anatomy - the scrotum. It is the external pouch of skin that holds the testicles. Full definition
She's an effective counterweight to the absurdity exuded by the two men in her life, as they scramble for her love and test to see who has the largest nut sack. (thecriticalcritics.com)
In Inside Job, fringed curtains pull away to reveal the most calligraphic nut sack you'll ever encounter. (dailyserving.com)