Saturday I took two of my daughters to see a musical at Harvard. Amazingly, in the small theater, we were in front of a pair of students who seemed intent on talking throughout the performance. (One male, one female; the male did seem to be doing more of the talking.) The volume seemed to increase until by the end of the first act they seemed to be talking at normal conversation level.
As soon as the curtain hit I turned and as nicely as I could (which was, probably, still with a snarl) that there were several bars and cafes available in Cambridge if they wanted to talk, but we were here to watch a show. I got several approving nods from around the nearby audience; in fact, about a minute later, an usher for the theater came over and appeared to be telling them to be quiet or get out, so others had clearly complained.
To their credit were apologetic and stayed quiet for the second act. I can only hope that I helped teach these students the important lesson that conversing in a theater is a very bad idea -- probably more important that most of what I ever teach in class. (Although how they managed to get this far without absorbing that lesson somewhere is, I admit, beyond me.) My older kids already know that, but they got some useful reinforcement.