Dumb things that you did.......because you didn't know any better.
Got a job pumping gas at the local Enco station. 14 years old.
I had tried to impress the boss with my mechaical skills but he kept me pumping gas (full service) for several months.
Then one Saturday I was told to help our lead mechanic on an oil change on a ‘53 Plymouth. Gene told me to check the transmission “grease”... so I got a 9/16” open end and pulled the DRAIN plug.
After I cleaned the shop floor(they were hospital clean 24/7) I pumped another several thousand gallons of Tiger Piss until I got a second chance.