I threw a weight in the distributor of my '68 GTO years ago. The weight jammed between the rotor and the housing and spun the entire distributor. It pulled all the sparkplug wires off and the engine shut down.

While this was going on, an extra rich mixture was being fed into the exhaust system. With one last spark, both of my Thrush header mufflers blew up. It split the seams in both mufflers, and opened them up like a gutted carp. Made quite a bang, too. I thought I just blew the whole engine.