NOW: Scrape off what you can without spreading the debris and dab the stain with a cloth dipped in club soda. If you can slip away to the bathroom, remove the garment, place a clean cloth on either side of the fabric, and blot from the inside. This will help force the stain toward the front, where it originally made contact with the fabric.
LATER: Pretreat with dish soap or laundry detergent, soak for 10 minutes, and launder in cool water. If the stain persists, apply a solution of two parts hydrogen peroxide and one part dish soap; let it sit for about an hour. Soak the garment in oxygen bleach for up to six hours, then wash again. If the stain is ground into upholstery, add a drop of dish soap to a damp towel. Gently rub in the direction of the fabric’s grain to work away the discoloration, then blot dry.