Cow Sack Share definition Flag An insult used to describe a person who pissed you off. Or to describe a slut who's gonna get pregnant at an early age. "Ugh, she's just never gonna give up! She such a cow sack!" Cow Sack by Floshanda June 16, 2015 0 0 Get merch Get the Cow Sack mug. Buy Now — $32.95 See more merch