I've posted this one before. My "personal worst":
I received a call upon my return to the office from a customer that wanted to know "What I'd done", as they'd lost power to a large section of their office.

I had been on a job walk in an adjacent building, and had taken a short cut through the customer's parking lot. They spotted my truck, and when they had trouble afterwards, figured that I must have been the culprit...S [Linked Image]

(I've also turned on water valves, etc. in places I've been working when coffeemakers and the like have not worked "It must be that electrician in the other end of the building")