Coffee fiends everywhere grapple with a familiar foe: stubborn stains on their favorite mugs. No matter how many times you run them through the dishwasher, those coffee stains just won't come clean.

If you don’t already own a Mr. Clean Magic Eraser, you need to drop what you’re doing right now and head straight to the supermarket, the drugstore, Amazon, whatever, and get one this very minute. The ...