That's how rubidium and cesium are described in this video about the explosive consequences of mixing alkali metals and water.
Gotta love the Brits. See also the competition between thermite and liquid nitrogen. Round two matches the winner against a Peugeot engine, and then the car's gas tank.
...Aaaand it's a fake. See here Theodore Gray's page for details.
Damn. I wondered how those glass ampules were opening in the bathtubs, and that pretty much answers it. I suppose I should turn this into an entry for Skeptics' Circle.