The worse bit of diy wiring I’ve ever seen was when we moved into a new council house with a garden in the early seventies. I was about 14 at the time. My dad went out and bought a secondhand 'home made' electric lawnmower from someone who lived in a block of flats. It was basically a cylinder push lawnmower that the bloke had mounted an electric motor on to, welded a couple of pulleys on it and connected them with a fan belt. However, the cable coming out of the motor (no switch, just connect up and go) went to a single socket outlet bolted to a piece of wood on the handle. Consequently, the extension lead had a three pin plug at either end! My dad was excitedly setting it up when he got it home and told me to plug it in indoors when I noticed that and told him it was dangerous. He told me not to be silly and touched the pins at his end and promptly got an electric shock. He still used it after that but plugged the lawnmower end of the cable in first!