Under-Onesie Share definition Flag The formation that occurs when a guy tucks his undershirt into his underwear. Nat, when you bend over, I can see your Under-Onesie. I guess your torso never gets cold. Under-Onesie by Ballsackreligious October 27, 2016 0 0 Get merch Get the Under-Onesie mug. Buy Now — $32.95 See more merch
