Onion Sweat Share definition Flag The nasty sweat from your balls that has the odor of onions. After I got done working out I threw my boxers in the wash, they smelled like onion sweat. Onion Sweat by afj21 October 30, 2006 0 0 Get merch Get the Onion Sweat mug. Buy Now — $32.95 See more merch