The materials:
Some sort of string or cord
Small piece of wood (not sure exactly what size, but scaled up to my hand in a pic)

Tools:
Saw
Drill (optional)

Step 1: How to Cut the "blade" to a Point

It's quite simple. All you need to do is make sure the points are on opposite sides.

Step 2: How to Make the Two Sides Face the Right Way

Again, it's really simple. They should be all spinning/facing counter-clockwise when it's thrown (for righties. For lefties, clockwise)

Step 3: Semi-Optional Step

If you want, you can drill a hole through the sides, which i did, but the more logical thing to do would be to make a clove hitch, frapping, tie it off with another clove hitch. But, again, i made the time-wasting choice and threaded it through the holes i drilled.

Step 4: Don't Be Stupid

Don't be stupid and throw this at people. This made a legitimate hole in my garage and would really hurt to be thrown at in the face. I'm not responsible for any injuries. Please, don't be stupid.