Ok, now the fun things.
Are you a Call of Duty fan and/or an office worker? If so, here is it. The office ballistic knife.
I'll make four steps: the Launcher, the Knives, the Loading and Firing, and the PSs.
Also go constructive with the comments.
Step 1: Launcher
a Pilot G2 pen
1)Disassemble the pen (note: to take off the spring, you can use a toothpick)
2)Saw off the pen tip
3)Insert in the back of the body the pieces in this order: Button, Spring, Piston
4)Screw back the top of the body
Step 2: Knives
some straws (just steal them from the canteen when no one's looking) (also, use the thin ones,not the McDonald's like)
some duct tape (usually found in the storage room)
some pushpins (one per straw)
1)Tape the pin to the straw
2)Align to the pen and cut as seen in the photo
Step 3: Loading and Shooting
1)Insert the knife
2)Press until you hear a "click" sound
3)Press the button!
Step 4: PSs
2- Move your arm fastly forward and stop fastly when you press the button
3- If you work in a hospital or similar, keep a straw excess to make a little shooter, like the one in the picture. Of course, you could also buy one at your local chemist's, but he might get suspectful if you ask him alot of these...