If you know how to, and if you practice, you can use playing cards a weapon. I am not going to teach you how to do that. In this Instructable I will show you how to throw them. Also, keep aware that you will destroy and lose many, many cards while doing this.
Just to mention, my camera is not great and I find it difficult to take photos with one hand, that is the wrong hand, and the camera is designed for the other hand.
*Ok guys, update! As it turns out, this way is wrong. It works, but is apparently my own adaption of a different way. Without overcomplicating it, your arm should be vertical, not horizontal.*
Step 1: The Basics
To hold it, grasp it between your thumb and middle finger, with your forefinger on the corner. Your two grasping fingers should be about 5 cm (2 inches) from the corner. This may sound confusing, but the pictures make more sense.
To start, you should sit on a chair, preferably a hard one. You should sit on the edge with your deck of cards on your lap. Start by holding your arm parallel to the ground. Your arm should be at a right-angle and be parallel to your torso. Bend back your wrist another 90 degrees so that it is pointing towards you. Yet again, this may all sound confusing, but the pictures explain it.