Video: Boom! Even if a feather dropped on or a mosquito landed on or like a heavy piece of dust managed to get on top of nitrogen triiodide, an immediate dark purple explosion happens. It's because nitrogen triiodide is so unstable that it detonates when it's disturbed, even slightly. Here's it firing off in slow motion.
Why does it do this? The Royal Institution explains:
Three iodine atoms cluster around one side of a nitrogen atom. Being crowded around one end causes something called bond strain as the atoms repel each other in a small space. The result is that the molecule is prone to falling apart, explosively.