I spend a lot of time in theatres (probably the only person not in the biz who does :P).
Here are some of my pet peeves.
Food in the theatre.
Unless it's dinner theatre, no one (least of all the actors) want to smell your dinner or hear you slurping/munching/crunching something. Trust me, your fellow theatre-goers are not happy (and one day you'll find one who isn't too gentle and will let you know to put your food somewhere other than your mouth). If you want the actors and ushers to LOVE you, wrap candies before hand in plastic wrap to avoid the crinkle.
Touching the stage.
I know it's tempting, but please don't touch the props, stage, *actors*. Some stages have wiring along the edges, so leaning against them will cause the play to go on in darkness. If an usher asks you to stop leaning and you persist, and if something then happens, you will be ratted out to the rest of the audience as being responsible. You do not want to see a pack of octogenarian ladies out for blood cause their favourite actor cannot perform (I can assure you, it's not a pretty sight). And I`ve seen actors get nasty if you are stupid enough to put your feet on stage, a foot away from the thespian. If an actor accidentally kicks or drops something on your foot, chances are you were somewhere you should not have been.
Tardiness.
I realize things happen. Screaming at an usher because you got lost, went to the wrong theatre, left at the last minute and ran into traffic, spent an hour looking for cheap parking in downtown Toronto, or lost track of time on a patio, will not win you any favours. IF it's possible for the usher to take you into the theatre, you will be allowed to go in and sit near the back. You will not be allowed to sit in your front row centre seats. 300 people arrived on time, you will not be allowed to disturb them, nor will you be allowed to annoy the actors on stage. Sometimes, you simply cannot go in to see the show late. Sorry. But if actors are running all around the theatre, in and out of exits, passing by patrons, it's simply too dangerous to enter the theatre. You may watch the performance on a monitor, until such time as it`s safe for you to be taken inside. Which might be intermission. And, no, you may not get a refund (by this point, box office is usually closed and ushers have no access to money or computers).
Electronic devices.
Not just cell phones or laptops or DVD players, all things that whistle, beep or emit light. You might think you`re being discrete, trust me, *everyone* knows where you are by the glowing light. And the ushers will not protect you from the rabid octogenarians. Trust me.
There`s more, but I`m already annoyed thinking of some of the neanderthals. Sigh. Must go play with the critters (who have more sense than some patrons). Even my cat has better manners (won`t say which one, but yes, he has been in a theatre, although he didn't get cast in the current run of Cats).
I should add that there are many, many wonderful people who go to the theatre. It's the 5% that stand out and ruin things.