Removing a coffee stain can be tricky, as the caffeine and sugar can often set in quickly. However, if you act fast, there are a few methods that might work. One is to try using a mixture of dish soap and ammonia. Another is to soak the stain in white vinegar for a few minutes before dabbing at it with a cloth. Be sure to read the labels on your cleaning products before using them, as some may damage the fabric of your bag.