Taking a seat properly in a movie theater should be one of the most easy things in the world but there are some who can ruin the whole movie experience for the masses. Here are the situations that most people find ridiculous in a movie theater setting.
Most people get bothered when a theater that is not very full because the movie showing is on a weekday during business hours, or the movie has been in the theater for a while and the popularity is dying and then a group of people sit right next to or right behind them when there are plenty of seats. People still need their personal bubble and by sitting right next to other people that are not associated with each other, that is plunging into their personal space. It is common courtesy to have at least a one seat space between and away from others when you are in a spacious theater. Enjoy your own personal space bubble and give people breathing room.
In a full theater things are going to get tight so if you are in a group make sure you group your seats by size of shoulders and alternate them accordingly since theater seats are only one step bigger then a plane, things are going to get cramped but if you alternate your group by wide shoulder, small shoulder, wide shoulder then this allow more room and a lot more comfortable. Be extremely courteous, obviously if you can get away with being one seat apart from other people then more power to you but in a premier showing you will not have this luxury so just keep calm and do not get anxious people are going to press up you a little bit whether you want to or not.
If you are the type of person who gets up a lot to sure the rest room, or for movie treats then be nice to other and taking a seat in an isle seat will be best. This way when you get up you are not blocking the screen or interrupting others.
If you are taking a seat then saving seats make sure you are only saving a few, 2 max per person to save seats the most unpleasant thing to see is 2 people saving 6 to 8 seats for people who have not even shown up to the theater yet when other patrons are there now. This is disrespectful to people if this showing is a sold out movie film and should not be tolerated.