Oh man. Early in my career I was working a job I didn't like and doing work that was by necessity incredibly hacky and tedious—not an interesting challenge, just a grinding one. It involved overwriting template files that weren't supposed to be overwritten and essentially writing multiple versions of the same code in multiple places because the system was so kludgey.
This project stretched on and on with brutally painstaking iteration, long hours, fires happening with other clients, etc, etc, long story short, I sort of lost my mind and left an Easter egg comment in the code in a state of minor madness.
Years after I had left the job, I got a message from a former coworker that said "Do you know anything about MOOL?"
I said I didn't know anything about something called MOOL, and he said, the client had found a long diatribe about a bovine god named MOOL in an obscure template file deep in the codebase, and I said, "ah, yeah, that was probably me."
The head of IT for the former client had found the code and gotten in touch with my coworker and said, "I assume this isn't a security breach, but I also don't know what the hell it is." He thankfully had a sense of humor about it, and it ended up being a nice opportunity to catch up. Pretty much the best possible outcome.
Now adays I would never do that, after experiencing real security breaches and dealing with that nightmare. But it was fun knowing A. My ancient horrible code was still in production and B. The comment I had left, which I'd forgotten about, and probably assumed no one would ever read, had been found like a flag in the moon or at least a time capsule.