One of my favourite explosive substances was Ammonium Tri-iodide which you can make (in small amounts !) by pouring strong ammonia over ground iodine crystals and filtering out the result. It's only really possible to do anything with it while it's still damp - when dry, it will detonate violently with the slightest friction - a small grain will make quite a loud crack - any larger amount can cause temporary deafness. One of my favourite uses was to mix it with grains of sugar on a piece of card and leave it near an ant's nest. The "advancing troops" would keep blowing up as they crossed the "minefield".
Another classic use was to paint small amounts on toilet seats (preferably in female toilets) the application of a posterior not only caused a small explosion, but usually left brown/purple stains around the cheeks.

We had an elderly aunt who stayed with us sometimes. She tended to be a bit nosey and would often poke around in the room which I shared with my brother, in spite of warnings from my mother. One day I had made quite a large quantity of Ammonium Tri-iodide and had left it on the filter paper rather too long. I was out at the bottom of the garden when I heard the bang. When I got into the house a completely paralysed aunt was staring at a cloud of purple iodine vapour and it took some time before my mother and I could get her moved to a chair for a restorative "cuppa". She was rather deaf for days - but she stopped poking around in our room. I was soundly reprimanded by my mother, but years later she told me that she had a hard job keeping a straight face !