I had a row of about eight youths in front of me at the movies once, and they were talking and laughing and that was fine, I'm not against people having fun. But then the movie started and they didn't stop. After about five minutes I figured that they just weren't going to settle down so I leaned in and said, not too loud, and not too fast, "Excuse me .... am I bothering you?"
They were nice and quiet for the rest of the show.