One we did to a friend years ago.
Here's the short version. I was at a friend's house (Jay) one afternoon goofing around with him and two other friends. It was the 4th of July and we had some fireworks to shoot off, mainly bottle rockets. Getting bored, Jay and I went into his shop and looked around for something to blow up. Jay grabbed a garbage bag and filled it with oxygen and acetylene from his welding tank. We tied that off, put it out in the back yard, and shot bottle rockets at it until it exploded. BOOM! It went off like an M80! Awesome fireball too.
We were to go to another friend's house (John) that night for a BBQ/yard party, plus we could watch the city fireworks from his back yard pretty well. We thought it would be great to pull a prank on our friend there, so we filled another bag with the gas mix, this time adding a lot more acetylene because, well, it sounded like a good idea. By now it was nearly dark. We then transported this bag full of death over to John's house in the back of Jay's Four Runner. That was super smart but we made it safely.
Three of us went to the back yard where John, his wife, and a few other people were. Jay snuck around and, in a dark corner of John's fenced in back yard (high wood fence) he quietly draped the bag of death over the side so it was in the back yard suspended from the fence about 5 feet off the ground. You couldn't see it at all.
Jay then came bopping into the party and for awhile we just hung out, drank beer and ate burgers, and shot some fireworks off now and then. Then it was time. Jay, me, and our to other accomplices loaded up our bottle rocket launchers, which by now we were deadly accurate with, and pointed them at the hidden bag of death. One of them hit the bag and ignited it. It did not blow up. No.
Instead, it just kind of went "Whoooooooooooooooosssssssssshhhhhhhh" and a HUGE ball of fire climbed into the air, catching his neighbor's tree on fire, John's fence on fire, and generally making a big ass fire. I scrambled for the garden hose and we got it under control after a minute or two.
Then I got to spend the rest of the weekend helping John fix his fence and cutting burned branches off his neighbor's tree before he noticed.
