One method is to spot-treat the culprit with a mixture of dishwashing liquid and glycerin ($4, walmart.com). Alternatively, try pretreating the blotch with a stain remover, a liquid laundry detergent, or a laundry-detergent booster, such as OxiClean Versatile Stain Remover ($5, drugstore.com).
Either way, follow-up by machine-washing your garment with the hottest water recommended for the fabric.
Have more stains to battle? Check out our favorite spot removers.