You can buy one of these cool rubber band machine guns (for $400), but that is not geeky enough. To qualify as a GeekDad you need the get the $30 plans and build it yourself.
The for-sale assembled gun — almost an art piece — has twelve barrels and loads 12 rubber bands for each barrel. That means that when you crank it you can launch an enemy-leveling barrage of 144 bands in a matter of seconds! As they say on their website:
The rubber band machine gun uses a similar mechanism to the famous Gatling Gun of the old west. It stands 40 inches tall and 44 inches from the handle to the tip of the barrels. The turret effortlessly spins a full 360 degrees and tilts from 45 degrees up to 22 degrees down so you can easily keep a moving target in your sights, no matter how they run. We keep one loaded in the office at all times to defend against hostile takeover attempts and pushy vendors.
The plans for the DYI rubber band machine gun are for a gun of a different design and lower capacity. It only holds 72 rubber bands, and looks a bit less elegant but to my eyes more military. Both contraptions are found on the same website, called Backyard Artillery. Indeed there’s a bunch of other cool geeky items.
One big caveat. I had not seen, used, or built either of these guns, or any other items on the site, so I can’t vouch for their performance. If you have experience with these or similar, let me know.