Ideal movie viewing can be compromised by people who constantly talk during a movie. Some other common problems are people who make phone calls and text, people who go to the bathroom 3 times during a movie, broken chairs, sticky floors, noisy babys, people who criticize or heckle a movie, and sitting too close to the screen.
I once heard that when famous movie critics like Roger Ebert review a movie, that the movie producers would make conditions comfortable for them so they could have an ideal movie viewing experience and hopefully give the movie a better rating. If that was true and I were a movie producer I'd include a foot massage and a fine meal as part of the movie review experience.
The worst possible scenario for watching a movie is when you are tired and falling asleep. This doesn't happen often in the theater, but anyone who has stayed up late trying to watch a DVD can relate to this. I hate it when I can't stay awake and doze off and have to rewind scenes or spend several nights trying to get through the same movie. No matter how good a movie may be, watching it while tired and fatigued can ruin the experience. I'm sure I have been critical of many movies over the years due to the fact that I tried watching them while I was falling asleep and had a bad experience.