ACOS Share definition Flag Ass Cheeks On Shoulders. Similar to head up your ass. An acronym used when someone does something stupid. Person A: "Whoops. Forgot to add a decimal point. Now I'm screwed." Person B: "What an ACOS move." ACOS by Besmgirl November 29, 2017 0 0 Get merch Get the ACOS mug. Buy Now — $32.95 See more merch