Step 1: Materials and Some Knoledge
A water bottle(0.5 liter poland spring is easiest to use)
The only reason the cap shoots off was because of the air pressure you created by twisting the bottom of the water bottle.
Step 2: Getting Started!!!
To make the next step easier, start pinching the area shown by the picture, on the Poland Spring water bottle, its the indented ring under the paper wrapper.
Step 3: Start Twisting!!!
The more you pinch, the harder and farther the bottle will shoot.
I didnt twist as much because I was only doing it for the instructable...
Step 4: Fire!!!
The cap should fly off with a loud(or kinda loud)pop. If it doesnt than you should practice the technique of flipping off the cap.
(Note: You cannot use the same bottle twice or you will not have the full effectz6)