When 10-year-olds (or at least, those with a mentality of a 10-year-old) over-react to a "scary" scene in a movie.
When I saw The Matrix in Miami back in '99, the theater had about 20 people in it. Perfect, I thought. About 30 minutes after the movie started, a couple of kids sat down two rows behind us.
Every time a fast-moving or action-packed scene fashed on the screen, two girls were screaming "EEEEEEAAAAK!" and crap. This continued until the last 15 minutes of the movie, when they were finally somewhat quiet. Point is, if you're not mature enough to handle violence and vulgar language, you shouldn't go to a an R-rated movie that's intended for a mature audience.
The other problem is cell phones. The latest trend is to ignore them ringing. Which is only halfway-polite when the ring is increasing in volume, persists for 60 seconds, and belts out some hideous melody. Your phone has a SILENT MODE, please learn how to use it, damn it.
I'd had it with movies at that point. I go to matinees only since then, and even then I'll only see 2-3 movies in the theater per year. With a DVD rental costing only $4 for an unlimited number of people, I can usually wait 4-6 months for it to arrive for home use.
That said, the Star Wars junkies are wierd, but at least they keep their mouths shut and cell phones off.