Six Stack Share definition Flag When a person is so fat he or she has six stacks of fat or six layers of fat stacked. The opposite of six pack abs. - David eats so much he has a six stack.- Dude you're growing a six stack. Six Stack by x_X_CerealKiller69_X_x June 18, 2011 0 0 Get merch Get the Six Stack mug. Buy Now — $32.95 See more merch