Lacking the ability to be safely be heated by a microwave oven. Things that have microwaveablelessness include 12 oz. soda cans, pressurized cans of R-12, chicken eggs in their shells, sealed film canisters filled with water, dry ice bombs, mercury thermometers, electronics, and lithium-ion batteries.
Saddam learned the hard way about the microwaveablelessness of a camping propane cylinder. He almost lost his house.