Nitrogen triiodide is the inorganic compound with the formula NI3. It is an extremely sensitive contact explosive: small quantities explode with a loud, sharp snap when touched even lightly, releasing a purple cloud of iodine vapor; it can even be detonated by alpha radiation. NI3 has a complex structural chemistry that is difficult to study because of the instability of the derivatives.
When I was studying chemistry at school, our teacher made some of this before a class and sprinkled it on the floor. As the students walked in, it exploded in little "cracks" under their shoes. The reason for doing that? Shit and giggles mainly. Everyone thought it was a hoot - it certainly got everyone engaged that day.
I imagine that would get you sacked and charged with about 50 OH&S and explosives offences these days.
The Modern Alchemist - Contact Explosive - detonating Nitrogen Triiodide from The Royal Institution on Vimeo.