Cant think of anything really daft that I've done, but many years back, my neighbor was a keen DIY'er, this included servicing, and minor repairs to his beloved Rover V8 SD1
He would nose the car up to the entrance to his garage, climb down into his pit, and proceed to pull the car over the pit, so he could do what was required.
This particular day, its believed that the exhaust was blowing on the Rover, so he went through his routine, and pulled the car over his head while he was in the pit, only this time he had the engine running... so he could find what was wrong with the exhaust? Unfortunately, one of the two garage doors blew shut behind the car, and locked in place, like it was supposed to do. trapping him under the car with the engine running... He died of Carbon monoxide poisoning, the car ran out of fuel, and was probably a full day before anyone found him!
Silly sod!
Thom