[True Brit]

Not the first, but probably the most embarrassing was a minor front-end rebuild on an MGC I had a number of years back.

I had just taken various bits out to be blasted and powder-coated, including the brake/clutch master cylinder brackets and cover, so the brake and clutch pedals were basically just hanging loose in the car. As the car was on a sloping driveway, I was pondering how to get it back into the garage for the evening (not enough room to work in it, you see). So I thought, "I know, I'll turn it over on the starter motor and crank it back in". Except I forgot to disconnect the coil lead....so you can guess what happened. It was on the choke, so it started almost straight away, in gear, went barrelling off into the garage with me hauling on the handbrake trying to stop it (don't know why I just didn't switch it off again!), and half-way out the other side as well.

Oops. Had to see the funny side of it. Fortunately the garage was built of wood.