tuna-slit Share definition Flag n. a cavernous, overused (and possibly scaled) vagina or fishy anus. Father Thompson, you can't stick that in my tuna-slit. It's not Christmas, yet. tuna-slit by MB87 September 29, 2010 0 0 Get merch Get the tuna-slit mug. Buy Now — $32.95 See more merch