Once at school I had arranged with another pupil that we would communicate over the short-wave at an agreed time, and I had a plunger in the garden. At exactly the moment that I received his transmission, I was to press the plunger. It all went pear-shaped because I never received his transmission. Bloody good job for the village hall though that I never pressed the plunger because it was wired up to a huge pile of sodium chlorate and sugar.
Later in life I managed to ignite a dustbin of explosive on the lawns of Girton College at 2am, but that was under military supervision.