These are good stories!
This one is more humorous than scary:
I had just built my first cart, and was anxious to go for a test run. I started it up (no brakes/no kill) and took off. The steering geometry was waaaay too quick, I could have burped and got sideways. I was headed for a tight spot between our swing-set and the drive shed - just enough room for the kart to fit through. I was really moving, and that; along with the 1/4 turn lock to lock steering the kart had - it was almost impossible to make small directional changes. I steered to avoid the swing set, went too far and was headed for the shed, panicked and over-corrected - now I was 6 feet from our jam packed plastic composter. There was no time, and no brakes, so I held on and blasted through that composter in an explosion of banana peels, coffee filters, and flying pieces of black plastic. The kart was undamaged, the composter was in thousand pieces spread over a 15 foot swath along with the contents there-of.
The wife was not pleased...