Where I work, a developer left an Easter Egg long ago where if you came to our ERP self service dashboard by way of 302 and had an expired SSO cookie, you'd be greeted by a little page saying "Dude, you got no cookie." Luckily it was a rare occurrence, and flew under the radar for a long long time.
Recently I reimplemented that middleware component. Part of the project requirement was removing that message. To keep the spirit of the Easter egg alive though, I have Dude you have no cookie written to the console instead. I feel good about what I've done. I think Easter Eggs in code are an important part of the job.
Does anyone have a story about an Easter Egg they've written or found that was particularly delightful?