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1.
The black discolouration that occurs on the bottom of one's foot due to the design of crocs whereby dirt enters through those stupid vent holes, but cannot escape once inside.

Sometimes it also makes your feet smelly- see croc rot
Is your foot frostbit like Mr. Deeds or do you just have Croc-Foot?
by Davey Crock-Footet September 12, 2011