grungy fucking Share definition Flag is when two people have sex without having bathed for day's. Nate and Jane went on a 3 day bus ride, then came home to have sex, without bathing first. This is called grungy Fucking. grungy fucking by LoveBunny1 January 12, 2014 0 0 Get merch Get the grungy fucking mug. Buy Now — $32.95 See more merch