foot mustard

When a foot fungus goes unchecked and starts secreting a strange yellow substance. That substance is called foot mustard.

Dude, get a doctor to check out your foot mustard situation, it's seriously gross.

Mustard Foot

To have smelly feet or some funky shit growing on your foot.

Damn, did you smell her feet in the car? Yea, that's some straight-up Mustard Foot dawg.