Most people know the "JUSTIN BAILEY" code for Metroid, which allows you to play the game as an unarmored Samus. But were you aware of the one which does no less than crash your whole system?
It's true. Entering "ENGAGE RIDLEY MOTHER F**KER" -- you can probably guess the missing letters -- will lock up most versions of Metroid. It'll crash the original NES version, reset Metroid Zero Mission and lock up your 3DS. If you do happen to "accidentally" type it in and your 3DS stops responding, simply eject the SD card and you should be fine. If not, it's the IT support desk standby for you -- turn it off and on again. If the power button doesn't immediately respond, holding it for up to 30 seconds will work eventually. Needless to say, if your 3DS ends up completely broken (it shouldn't) then we accept absolutely no responsibility for you typing that filthy code in, you pottymouth.
The "NARPAS SWORD" and "JUSTIN BAILEY" codes both work in the 3DS version of Metroid, so when you're done giggling like a child at typing rude words into the password screen you can then cheat your way through the game with a semi-naked Samus, too. Have fun with that.