People who get up more than once to get food during a movie. You're there to watch a film, not to eat non-stop.
People who make loud rustling noises during "quiet" moments in the film. Keep your damn popcorn, chocolate bar or mints still until it's over.
People who bring smelly food from home or a restaurant to the movies. I actually had an entire family eat dinner -- garlicky, stinky Chinese food -- behind me at a movie. I like garlic, but I don't like it THAT much.
People who slurp their drinks, then let them roll on the floor even when there's still liquid and ice left in them. Learn some manners!