My own "favourite mistake" was the time I had a service change one morning. I got there early, set up, and was all ready to cut the wires when the homeowner came out and askd "Who are you and what are you doing?" OOPS- I was off one street, in a place where two streets were only every so slightly different in name!
I packed up, with apologies, and got to the right place on time. Set up, was just about to cut the wires, and ....BANG...BANG, followed very quickly by a zip zip as the bullets went whizzing by.

That day was wasted, as police dealt with a barricaded gunman, and my truck was wrapped in crime scene tape. The gent had taken exception to a traffic stop, had raced home, and in the drama that followed, killed one of the cops- whose last words were "come on out- we only want to talk to you!"
By the way, this is the ONLY service change where it hasn't rained on me!