Nitrogen triiodide is an unstable chemical so reactive that the slightest touch can set it off, even from a stray radioactive alpha particle. A feather, a mosquito, or a gust of air can also make it burst. When it explodes, it goes BIG, travelling at over 7,000 miles per hour.
It's made by exposing boron nitride to iodine monofluoride in a carbon-fluoride-chroline solution at low temperatures, refining into the nitrogen triiodide, which is (just as it sounds) one nitrogen atom and three iodine. It has a small handful of uses: it's used to kill microrganisms in flour and on melons; to clean out semiconductors; and as a fuel oxidizer.
This video from the Royal Institution shows the real use for it, though: doing awesome explosions, then breaking down the frames in slow-mo. There's plenty of "what will set this off?" including air and balloons. There are just as many great explosions with purple clouds of destruction. Blah blah blah don't try this at home.