I was upgrading a clients server. All was done and I was going to pull a new back up after a reboot to check that it would auto start like it should. Everything was working perfectly so I deleted the latest backup (to make space for a fresh one) and restarted the server to begin the new backup.
The entire system had been in service for a year without any trouble and I had just changed some software, nothing too serious. For some reason, upon last reset the mainboard corrupted the hard disk data. Gone, done. Come to find out, the other backups from just days before were no good due to his employees). Just goes to show, you never know how good your backup is, until you need it.
This happened on Friday at 9pm. I had until Monday 6am to have it fixed or the company would have employees in several states not able to work. Luckily, I recovered the old data from the system I had it all back up on and deleted (good disaster recovery software is always a good thing). Everything worked out in the end luckily.
Odd thing is, I have messed with the hard disk and the motherboard in other boxes and never had the problem again. A better backup system has now been installed (3 in fact) and I don't delete anything until another backup is made and verified.
A few from when I was in the Air Force.
I knew a guy who despite being told, washed the canopy on an F-16 fighter jet with citrus cleaner... Which just so happens to eat the nuclear flash/radiation protection from it and can craze the canopy. I do not remember the price tag, but it was more than he made for his entire enlistment.
Another guy pushed a wing into the hangar doors, no damage to the jet other than a wing tip light and a dent in the hangar door.
Or the guy who basically bleached the entire paintjob on his F-111 trying to get it clean...