Scrape excess mustard from the surface of your shoes with the edge of a spoon. Wipe the mustard onto a paper towel and discard.
Place a few drops of glycerin on the remaining mustard stain. Rub the glycerin into the shoe material. Allow it to remain on the surface of your shoes for one hour.
Press a paper towel into the stain to absorb the glyerin and loosened mustard. Move to a clean portion of the paper towel and continue to blot to get as much mustard stain off your shoes as possible.
Pour 1/2 teaspoon of dishwashing detergent into a bowl. Add 1 cup of warm water and three drops of white vinegar. Wet a sponge with the detergent solution. Squeeze the sponge to remove excess moisture so the sponge is barely damp.
Dab at the mustard stain with the detergent solution to remove the rest of it. Follow by blotting your shoe with a dry cloth to absorb the stain.
Rinse the surface of your shoe by sponging it with a damp cloth. Absorb excess moisture by pressing a dry cloth into the shoe surface. Allow your shoes to air-dry completely.