Worst one I did when working at Peugeot is when on ramp was lifting the car and was not correctly on and it fell off on to my mentors tool box. But I was 16 lol Resent things o done I done is the old where my tool in my hand trick. Looking for parts when you fort you removed but are still on the car. i done so much over the years of being a mechanic it amazing how little distractions can make us do silly mistakes