tit stain Share definition Flag the moist line a fat girl gets between her gut and tits when she sweats. this usually occurs on a hot day. extremely noticable when a bigger girl wears a smaller shirt. dang...you know its hot out when the big'ns have tit stains. tit stain by heatmat August 30, 2006 0 0 Get merch Get the tit stain mug. Buy Now — $32.95 See more merch