Happy be-lated Birthday, Ross!
My submission falls under, "I'm breaking the game and scaring the devs".
The game is, Marvel Heroes 2015, an MMORPG based on the Marvel comics.
The "breaking" happens within the zone called, SHIELD solo-sim. You just fight wave after wave, gaining gear, unlocking achievements, and proving you're a badass. However, it's programed to randomly insert sims you can't win. Basically, teaching the player you can't always win and dishing out a harsh sense of reality.
Built similar to the fabled sim in Star Trek, like Kirk, you need to "think around" the program.
Knowing your abilities/powers, or through sheer dumb luck, you can push through the impossible sims and win. No big deal, right? Now, keeping pushing through and winning and watch the game lose its mind!
Mobs start to freeze so they're easier to kill, chests release fountains of gear, the dialogue appears scrambled, etc. I was able to push the sim until the game crashed!
Supposedly, the devs know about this but nothing has been done. I doubt that they do, or this would have been patched out long ago.
For now, I'm happily collecting the best gear in the game until it crashes ;D