This is a neat trick that will cause severe pain, and a red mark. You don't really need much for this, a stick of Big Red, some saliva, and a high tolerance to pain.
-A stick of Big Red Brand chewing gum
-The wrapper from the gum
Step 1: Unwrap the Gum
Very easy, simply unfold the tabs on the wrapper and remove the stick of gum
Step 2: Chew the Gum
Take the stick of gum you removed from the wrapper (Don't place the wrapper in your mouth), place it in your mouth, and chew. Don't do this in any other order no matter how funny it may seem.
Step 3: Chew the Gum for 3 Minutes
Move your lower jaw up and down, with the gum in your mouth for three minutes. Enjoy the flavour, it is good gum.
Step 4: Lick the Wrapper
Take the wrapper (you saved it didn't you?) Lick it then stick it to your forehead.
Step 5: It's Gonna Hurt
It won't hurt right away. Give it about 30 seconds.
Use it how ever you see fit, but remember, it's only funny when it hurts your friend, not you.