Place a layer of paper towels over the coffee spill. Press your hands or feet onto the paper towels to absorb the coffee from the floor mat. Discard soiled towels and repeat this step with clean towels until no further coffee is absorbed.
Pour 2 cups of warm water into a bucket. Add 1 tbsp. each of dishwashing detergent and white vinegar. Stir the three ingredients together to mix them well.
Wet a clean cloth with the detergent and vinegar solution. Wring out the cloth to remove excess moisture.
Sponge the floor mat with the cloth to remove the remaining coffee stain and odor. Rinse the cloth as the coffee is removed. Apply more detergent and vinegar solution and continue to dab at the stain.
Dampen another cloth with water. Blot the floor mat to rinse the detergent off.
Moisten a dry cloth with 3 percent hydrogen peroxide. Test an inconspicuous area of the carpet to ensure the peroxide doesn't cause the fibers to become faded or discolored. Blot the stained portion of the floor mat with the peroxide to remove any last traces of coffee stains. Allow the floor mat to air-dry.
Rinse the floor mat by sponging it with water. Allow the mat to air-dry completely.