Bank Security
Many many moons ago (1990 in fact) I was working part time at a local bank doing filing and what-not in the loan securities dept (You know, where the stuff you secure your loan with gets kept. Gold/Stock sertificates and the like).
The combination on most (99%+) "High Security Cabinets" was the factory default of 10-20-30-40.....
When the bank got amalgamated with a few other banks a while later, I got the job of getting all the securities documents from one of the other banks (this was mostly for motor loans) and bring them (and file them) at our offices.
Get to the other banks site and naturally all the cabinets are locked and there is nobody there who knows the combination. I thought to myself "Surely not".... Guess what. It surely was. I was able to open 20 out of 21 cabinets with the SAME damn combination (to the absolute HORROR of the branch manager).
There were some erm "firm" words spoken about security the next day apparently :)
Good times.