How to kill a fly without a flyswatter...

1.) Position your hands a few inches above the fly as if you were about to clap.
2.) Clap.
3.) Wash hands.

Detailed instruction:

Flies. They have to be one of the most annoying and useless of all of nature’s creations. They don’t bite or sting you. They don’t suck your blood or carry the West Nile virus. All they do is throw up on everything they land on. For such an overall worthless creature, though, they were certainly equipped with some pretty amazing survival skills. With all those eyes, slow-motion vision and wings, they are probably the most difficult insect in the world to kill. That’s why we invented the flyswatter, an incredibly effective tool in fly assassination, but an otherwise useless piece of plastic. And who ever really has one handy when there’s a fly bugging the hell out of you, anyways? After stumbling across an interesting fact about flies from an old friend, I spent years perfecting my chopstick-free technique for killing a fly with your bare hands anywhere, under any circumstances, which I will reveal now.

Step One
Understand their weakness:
One of the interesting things about flies is that when they take off from a surface, they fly straight upwards for just a moment before they can go any other direction. This leaves them particularly vulnerable for the first few inches of flight time before they orient themselves and become nearly impossible to kill. The trick is to catch them during this weak moment.

Step Two
Setting the trap:
Let’s just say a fly lands on your leg. Position your hands, palms facing each other about 3 to 4 inches apart, as though you were about to clap. Very slowly, move your hands in this position towards the fly until they are about 3 to 4 inches above the fly, which should be centered between the palms of your hands. If you don’t move slow enough getting to this point, you will scare the fly away, but don’t be discouraged, it does take practice, and if you wait long enough, it’ll be back.

Step Three
The Coup de Grâce:
Once you’ve got your hands in position (make sure hands aren’t too far apart or to far from the fly, otherwise it will escape your trap), clap your hands once firmly. When you open them you should have a dead fly on your hands, pun intended. After a little practice, you’ll rarely miss.