"Luckily I think I can answer this using the same project! The best/worst Arduino creation was an open-source Homeland Security non-lethal weapon project: "THE BEDAZZLER: A Do-it-yourself Handheld LED-Incapacitator".
"After attending a conference where the $1 million "sea-sick flashlight" (named "THE DAZZLER") was demonstrated by the US Department of Homeland Security, we decided to create our own version using an Arduino. For under $250, you can build your own dazzler and we've released the source code, schematics and PCB files to make it easy. A great Arduino project for people who really like blinking LEDs. We also added in a mode selection so you can put it into some pretty color-swirl modes, great for raves and parties!"
Making It Work
Before you start messing with an Arduino board, you will need to learn how to program one. Luckily, there are a number of resources that can help you get started.
Ladyada has a few suggestions:
"A lot of people use my free tutorials on my personal website. "I have six lessons all together and many people over the years have said their is where they started their journey. There are also some great books, two of my favorites are: Getting Started with Arduino By Massimo Banzi and Practical Arduino by Jon Oxer & Hugh Blemings. The free open-source Arduino IDE (how you program Arduinos) also has tons of code examples and libraries.
"Next up, there are Hackerspaces for in-person learning and workshops and lastly (but not least) the amazing Arduino online community. You can visit the arduino.cc forums or Adafruit forums and see thousands of people helping each other and sharing code! It's a wonderful community and very inclusive to beginners!"