eff that Share definition Flag A way of saying "Fuck that" without using the actual "F word." Used by many "edgy" teens, attempting to appear hipster and rebellious. Person A: We have 5 hours of HW Person B: Eff that eff that by gtweak November 5, 2013 0 0 Get merch Get the eff that mug. Buy Now — $32.95 See more merch