10-90 Share definition Flag The truest form of the mullet, it contains 10 percent of hair on top and 90 percent in the back. Did you see that guy driving the Camaro. No, why? He had a sweet 10/90. 10-90 by CyberC November 11, 2003 0 0 Get merch Get the 10-90 mug. Buy Now — $32.95 See more merch