Fill a large plastic bag (be sure to check for holes first!) with several cups of vinegar and secure it to the showerhead with a strong rubber band. For the best results, leave it overnight and remove the bag in the morning. Then, give your shower head a quick wipe-down with a dampened washcloth.
All you have to do is add some uncooked white rice to your coffee grinder—about the same amount of coffee grinds you would normally add. Allow the grinder to pulverize the rice, and the grains will remove the stink as they exit the grinder.