Fake Brick 3DS
From GameBrew - a wiki dedicated to Video Game Homebrew.
This is admittedly not a very useful homebrew, but I just made it for fun. Basically you can run it on someone's 3DS and it simulates the screen that appears when it's bricked, so you can scare them.
I created this using Steveice10's Homebrew Template (https://github.com/Steveice10/3DSHomebrewTemplate) and I didn't change the readme or anything, in case you're confused.
This includes the source code as well as all the standard binary formats (in the "output" folder). Let me know if you prank someone with this; I'd be curious how they react!