How can you think it makes you cool to whisper with your friends while other people, who have worked hard all semester to learn this music, sing on stage? Does it make you funny to clap once after everyone else has finished clapping? Are you popular for twittering and giggling during a concert?
No. You are just being an imbecile. Yes, cultural events are required for students. Sometimes you don't want to be there. That does not give you the right to be a jerk. Until you're the one on the stage, you don't have the privilege of judging a wrong note or a style different then what you are used to.
The students who perform in these concerts and plays and such have spent untold hours learning their music, lines, etc. They have put all their effort into their work. How do you think it makes them feel when you can't keep your comments and laughter to yourself or your cell phone off?
So please. Straighten up or get out of the auditorium.