I had one of the worst experiences in a movie theater this weekend. The movie was excellent (Mission Impossible: Ghost Protocol - go see it) but the audience was scarier than Jason and Freddy fighting to your death.
Not only did people not move over, making the task of finding a seat nearly impossible, but the people sitting around us would not shut up. At all. Through the whole movie. Add to that the fact that they kept getting up and climbing over each other to leave the theater or change seats (and hitting my chair while they did so) - I was ready to go ghost protocol on them.
You're in a movie theater. The whole purpose is to watch the freakin' movie. Don't talk. Don't get on your phone. Don't get up and leave (unless you need to talk or get on your phone; in that case, don't come back til you're done).
While you're at it...
Chew with your mouth closed...don't hog the arm wrest (especially if the person next to you is not your date or friend)...unwrap noisy candy packages before the movie starts...don't burp...or fart...sit still and be quiet.
Basically, act like you didn't grow up living in a barn with other animals. Behave in a way that your mom wouldn't want to disavow you.