Once I worked on a custom CMS for a client who was really into breaking stuff... actualy he broke a lot of shit by doing some stuff on he's website while it was live!!!

Once after a hard days of work I had to publish the new version of the site...... first I checked that it is still working on the live server so I could take a backup.... gues what the website was totally fucked up......
I was really angry at that moment and this incident wasn't the first one so I created a user with bunch of swear words as name, surname, email etc etc... and I forgot about it..... so 2 to 3 weeks later the client noticed that user.... and wrote a angry letter to my boss....

Didn't get fired tho :D