I had a client who had prod database access due to it being hosted internally. They called up saying "their system is no longer working".

After about an hour of investigation, I find one of the primary database tables is empty - completely blank.

I then spend the next hour looking through code to see if there's any chance of a bug that would wipe their data and couldn't find anything that would do that.

I then had to make "the phone call" to the client saying that their primary data table had been wiped and I didn't know what we did wrong.

Their response: "Oh I wrote a query and accidentally did that, but thought I stopped it".