I once (almost) sent the wrong advert to air.
Luckily, here in the UK, every TVC needs to be cleared by a standards body before it is allowed to go on, for technical and ethical standards. As part of this a transcription needs to be made.
In this case the ad was for a comedian whose thick northern accent couldn't be deciphered by the South African producer. She turned to another producer to ask what he was saying and a senior producer happened to walk past at the same time.
"That's not the right joke..."
Having already gone home for the day, I got a stressed late night phone call demanding where the correct timeline was. The whole thing had just been a communication error, but I felt like a dunce.
Another time a junior editor I was working with came back from a shoot with a production drive full of footage, plugged it in and (presumably without thinking!) immediately reformatted the drive.
Luckily the cameraman had a back up, so we sent the junior on a 3 hour round trip to fix his mistake.
I'm sure you have your own stories to tell too but thankfully we are not alone.