How do you get coffee stains out of a stainless steel mug?

Fill a bowl with a chlorine bleach/warm water mix and drop the mug in the bowl and soak for about an hour. When finished, rinse the mug thoroughly in cold water. It should remove the coffee stains and bring the mug back to it's former glory. The same trick works well for cleaning stainless steel cutlery as well as porcelain cups and mugs.

Try baking soda & water, leave it sit on the stains for awhile, then, scrub them off.

I scrub it with a bottle brush............but I never can get all of the out all of the coffee stain, but I get most of it.