On the audience front, there are the mishaps and emergencies that can't be avoided. I remember curling up to watch Interview with the Vampire for the second time at an old rep theater when a man had such a big seizure that the girls in front of him were covered in saliva, and everyone was in a panic thinking he was dying (he wasn't). And that's only the tip of the potential physical issues that can pop up, from heart-attacks to water-breaking labor. (Thankfully, I've never had to contend with those.)
But movie theater issues aren't only about patrons ...
Sometimes someone was smoking up and not paying attention to what order the reels should be in, and soon you're a time-traveling audience member, knowing what happens at the end of the film before the middle. Or, someone didn't spool the film the right way so that just as things start heating up in Brokeback Mountain, about an hour in, the movie flips and starts playing upside down, meaning we all had to come back to see it all again. And sometimes it's entirely out of the theater's control -- like a packed showing of Blade when the power went out for 20 minutes mid-film, not to mention the times some jerk pulls a fire alarm and everyone has to evacuate.
Basically, as crappy as it is, some form of cinematic bad luck is destined to happen to all of us. I've shared some of my worst experiences ... but what are yours?