At my first job, I got tired of having to type a user name and password every time I debugged the web application. Thinking I was clever, I put in a hack so that if you launched the application with the query string "?user=Administrator" it would log you in as the administrator. So much typing saved!

A couple days after the next release, I realized it shipped like that. In absolute horror, I walked into my boss' office, closed the door, and told him the tale of my mistake.

He just looked back at me, and after a moment or two said, "Loose lips sink ships."

And that was it.