There was one tester we all hated, because, well she was just insane. Some developers had email filters that moved her messages to the trash. She was so gone, that she couldn't comprehend the difference between her just thinking something to herself and actually communicating it to someone else.

One day, a coworker and I decided that she was so close to the edge, that we could probably drive her over it.

We placed a little toy called "Gremlin" in the build, with some code that made sure it was shut off, except in the case of our friend, the "Testy Tester." What Gremlin did at random intervals was to have a weird little yellow/green guy grab the bottom of a window (as if the 'window' was a window into his room) and pull himself up to peep in and wave "hi" at you.

This was all fine and dandy in testing. Unfortunately, when the app made it out to production, heavy network made the client take six times as long to finish user authentication. Since we had the conditional shutoff code in the user authentication, this gave a chance for the Gremlin to wave "hi" at some of the users in the login dialog.

Whoops.