Given the widespread availability of 12 oz. soda
cans, I supposed it was only a matter of time before someone
determined how to tap the tremenous energy contained within those little buggers.
You will need a thumbtack with a little handle thing (so you can remove and insert it easily), and an unopened can of some carbonated beverage, preferably something sticky and colorful, like Mountain Dew or Slice. To prepare your weapon of mass destruction, look at the top of the soda can. Notice the pull-tab at the top, and now notice where it pivots, that is, there should be a small, circular piece of metal that attaches the tab to the top of the can, and it protudes slightly higher than the tab itself.
Found it? Good. Carefully insert the thumbtack into this piece of metal, puncturing it. This is actually the softest area on the top of the can, you may need to put some muscle into it, but be careful you don't let the can fly out of your hand (or insanity will ensue - maybe). Once the tack is inserted, hold the can in your palm and place your thumb on top of the tack to hold it in place (the resulting build up of pressure would force it out otherwise, sending tack and soda into your face, very embarrassing). Now, get ready, shake the can vigorously maintaining a tight grip on the tack.
Now, you're ready to strike. Point the can at your target, and quickly remove the tack. A thin, deadly stream of soda will issue forth with very good accuracy. Don't let it go for too long, though. Place your thumb over the hole and shake it up some more before spraying it anymore, or hold it there to keep the weapon intact. Shoot it at your friends, shoot it at your enemies, shoot at random passing cars, or shoot it in your mouth, it's fun fun fun!
Note that this will only work as long as there is enough carbonation in the liquid to force it up against the hole, and enough liquid to fill the space in the top of the can. Once you've ejected about 1/3 of the total volume of the can, your weapon will being to fizz out. At this point, you might want to just drink your soda, although it will be quite flat (an unfortunate side effect).
Fine print: I take no responsibility for any damages incurred as a result of using this technology. Seriously. One year at summer camp I bought a soda at the machine and squirted it at a car in the parking lot. Some jerk snitched on me and I had to pay $10 for the owner to get his car washed, no joke. So, wield this power wisely.