When your socks are so old and ratty that the toes curl up into a pointy, paper thin strip of material composed primarily of toe jam, decomposing cotton, grease and floor dirt, dead skin and toe nail cells. The end result looks like the unfortunate foot from a Dr Suess character.
Person 1: "Dude, Josh hasn't changed his socks in days. Those grinch toes are gnarly."
Person 2: "That's unfortunate. Change your socks you grinchy fuck!"