I think in Beta 1.8_1 (or 1.0.0, but I think it's 1.8_1), Herobrine.
I had SPC on, and just felt like teleporting to a random place.
Typed in something, I forgot (._.'), and I got teleported.
I got teleported into a swamp, and never seeing a swamp, I decided to
explore.
As I walked around, it seemed like a decent place to settle.
Nice forest, tons of animals, and a giant bedrock wall.
The giant bedrock wall scared me, I had never seen anything like it
before. I decided to explore that, with the /fly command.
Seeing over it, I saw pyramids. Two seconds later,
I'm deleting the world.
END OF STORY (p.s. TRUE STORY, sorry, I'm starting to be like those 'HEROBRINE IS REAL DERR' people..not sure if this happened to anyone else.)