Dr. B's Finest Kind Medical clinic and Fish Market

Fill a clean mug about 1/3 full of clean water (DON'T FILL IT TO THE TOP!), then heat it for about three minutes in the microwave oven. Now carefully take it out and immediately plunk it firmly onto the tabletop (whack it hard, but not so hard that it breaks.) The boiling water will burst into froth. DON'T BURN YOURSELF! The superheated water acts almost like warm carbonated cola: if you strike the container, it will foam up instantly.

Another trick: heat up the water to boiling again, remove it from the oven, then immediately insert a dry wooden coffee-stirrer or a wooden popcicle stick into the water. Foosh! The water boils violently. The dry wood contributes a layer of air to the water, and the air fills with steam and expands into a mass of hot foam. ............

 Don't dump any sugar in a mug of superheated coffee, or the spewing foam *really* gets violent.

and if you think coffee explosions on your kitchen table are bad, think about this:
 PS
Certain types of foods have no bubbles inside, and these foods will superheat and "explode." For example, never cook a whole unbroken egg in a microwave oven. The explosion isn't just messy, sometimes it's violent enough to smash up the inside of your oven or tear off the door. Paste-like canned foods easily superheat since they're too thick to allow streams of tiny bubbles to form. Canned spaghetti sauce is famous for superheating and causing those "BOOMF" mini-explosions that spray the sauce all over the oven. (I wonder if there's any cure for the "Spaghetti-O explosions?" Maybe whip the stuff with a fork before cooking, so lots of air is added? Mix it with dry bread crumbs or other material that's full of air?)

Martha Stewart, call your office....