Step 1: Get a Gatorade Cap
Step 2: Now Hold It Like This
Step 3: Aim It, Then Flick It.
I told you this was a simple instructable... I don't know why so many people ask me how to do this.
Try doing this at school, and have it land in the trash can, or see who's goes the furthest, or hit that poster with Einstien on it. Or maybe the teacher.
After a while of doing this, your middle finger may hurt.