Things You Can Do With Absolutely Nothing When You're Bored

Push your eyes for interesting light show (Amusement Potential: 1-5
minutes) See a variety of blobs, stars and flashes. Try to make out
things-is your subconscience trying to send you a message? Can you 
control what you see by pressing different areas with different 
forces? Would it be possible to somehow see the same effects on TV? 

See how long you can hold your breath(Amusement Potential: 4-20 minutes)
Not that much fun, but it sure passes the time. Play with a friend, or 
try to beat your own personal best. Some tips: hyperventilate before 
hand, and stay as still as possible. My personal best is 2:00 (exactly). 

Try to not think about polar bears specially hard, because by trying 
too much, you remember what you were trying to avoid thinking of. 
If you try too little, you end up thinking about polar bears anyway. 

Scratch yourself 
(Amusement Potential: 1-3 minutes) Go ahead, scratch yourself now. Even 
if nothing itches, go ahead. Doesn't that feel pretty good? 

Hurt yourself 
(Amusement Potential: 1-3 minutes) What is pain? Why is it unpleasant?
There's nothing physical about it - it's all in your mind. Plus, after
pinching yourself for awhile, boredom will seem nice next to being in
pain. 

Try to swallow your tongue 
(Amusement Potential: 1-3 minutes) There's not much to say about this 
one. It is possible. 

Get yourself as nauseated as possible 
(Amusement Potential: 5-10 minutes) Best achieved by looking straight up
and spinning around. Try to be so dizzy you can't even stand up. This is
also entertaining due to the "makes boredom seem a lot better" effect
(see"Hurt Yourself").