Among destructive devices built as kids in the 90s, I think our crowning accomplishment was the Thermite we made as teenagers... only possible thanks to my friend who was somehow able to acquire a big block of Magnesium. I provided the Aluminium baseball bat ;) We got lucky that it fizzled out partway through (maybe from hitting dirt?), but his parents were definitely not too thrilled about the nasty hole in the concrete patio.