He has put a lot of thought into the optimal way to blow up a microwave, and has settled on blowing it up by putting a bottle of sealed liquid in the microwave and turning it on (and leaving the room). In this video -- the latest in a series -- he experiments with a Kahlua bottle that he's sealed with silicone, and manages to produce an explosion that shocks even him.
Here on Reddit, he describes the delicious sense of suspense he experiences while waiting for the microwave to blow: "The sound when these things explode is hard to describe, it's a very loud low frequency WHUMP, very unlike a gunshot or chemical explosion. I've only ever heard it from the next room, so I can't imagine how loud it is in the room! The wait is the killer, you have no idea when it's going to happen, just that it takes approximately 20 minutes. As Adam Savage said, that kind of stress cannot be good for you!"
Needless to say, you shouldn't try this at home, or anywhere else.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.