Far from the most stupid thing I've done - merely "one of the stupid things I've done recently"...
Had been balancing and painting my old 2.8m (10') prop. It was outside, and was just on a fairly flimsy, lightweight support to allow me to turn it freely to balance, and turn while painting...
Just a very mild breeze - barely enough to blow the paint fumes. So I'd taken off the stay so I could turn the blades to make it easier to paint.
The breeze picked up a bit, and before long it was a moderate breeze, probably 10mph or so. I thought I'd just let it turn a couple of times and see how it looked.
I didn't expect it to spin up anywhere NEAR as quickly as it did. On needle-rollers it was very free... and the blades are solid fibreglass - several kilograms each. In seconds it was far too fast to stop. It was such a flimsy mounting I didn't dare risk trying to turn it out of the wind (gyroscopic forces would likely have just broken the pin off).
Blind panic set in, I lost skin and got quite bruised, but brought it (just!) back under control by trying to grab hold of the blades back at the root and slowing it down fractionally, and moving slowly out along the blades until I could get it under control.
Never again. Nup, no way.