When my dad was a kid, he wanted to make "rocket candy" (solid rocket fuel made from sugar and saltpeter), so he melted sugar in one saucepan, saltpeter in another, and then tried pouring one into the other. However, it ignited on contact, and rapidly combusted, making a big noise and a charred mark on the ceiling.

I guess he should've only melted the sugar and not the saltpeter

Or maybe he was melting them together and heated the mixture up too much? I forgot the details

@wolf480pl I actually did this exact experiment when I was a kid. Made a smoke bomb to flush out a woodchuck from it's hole. It worked pretty well but man did that mixture burn hot. I had to stamp out some tall grasses that started catching fire around the area I ignited it.