The first motor I ever changed was in my first car. '73 Chevelle, (couldn't have been '72). I bought a short block from a rebuilder. Brought my new/rebuilt piece home in the back of my buddies truck. We didn't have a garage but there was a room on the end of his mom's house we were going to finish building it in.
We get home and we are just going to lift it out and carry it inside. He has me back up close to the door. I'm backing up slowly, which was too slow for him. He gives me the big come on hand wave and yells back up, so I start heading back quite a bit faster watching him not where I'm at. Well I am getting close fast so he panicks and yells
STOP. Yeah you guessed it, out on the concrete driveway it goes.

ops:

ops: I couldn't believe it didn't land on the deck or anything just messed up the belhousing mount a little. Well you live you learn. Usually the hard way.
Same friend same place we are putting a lift kit on his new Ford truck. Of course we have it jacked up a mile and held up by the safest concrete blocks we could find. We are under it working away, the u-bolts have to be torqued to 150lbs-ft. I say, "did you hear that?" We stop for a second and there is another creaking sound. We fly out from under it just as it falls to the side and to the ground.
Same truck he is changing the intake to a performer and has his hood laying in the yard. Some people come over and my car is blocked in the driveway. That night when I leave I pull through the yard not able to see the black hood laying on the ground. Made a sick crunch as I ran over it!
A tornado came through a few weeks later and threw someones roof on top of the truck so the insurance company took care of my screw up.
Luckily we just laugh about that crap nowadays.