Recently wrote a script that would check 2 years worth of images, crop them, and resize to different sizes as changes to front end required those.

Eventually the script went into an infinite loop and crashed the whole CMS.
The worst part was that my manager was on a date and I had to call him back into office, since his laptop was still at the office.

The actual problem wasn't the loop.. I forgot to check if file actually exists before cropping... Error log size was 10gb!