The four ladies seated behind my friend and I last night at the theater. This was a funky dance company, and as soon as they were seated, the yammering and screeching began. And the taking of selfies, and so on. Ok fine. but it continued when the lights went off, and the music started. I could still hear them over it all, and while I totally admit I could have been a tad more polite, it just popped out. It's only recently I've been able to ask someone to please keep it down in a theater or other setting.
I turned around and said "I'm sorry, could you please be quiet?" Again, could have said it a bit more politely...one said sorry, but the other said "Really?" Again, this just popped out (my mouth moves faster than my brain sometimes, but I'm working on that) but I turned around and said "yes. really" They did keep quiet throughout the performance though.