Guideline for Civilized Interaction #34 :
When entering a space designed to hold a large number of things, be it a parking lot, or a movie theater, or the like - and it is currently occupied by very few things, take it upon yourself to park/sit somewhere other than right next to someone who’s already there.
Witness : I went to Anchorman on Tuesday, intending to enjoy the film before it left theaters. And it was a very good movie. I was the first person in the theater. The only OTHER people to come in were a family of four. Who sat down behind me. Who had babbling children. Who’s father had emphysema or something. And who had come fresh from shopping in whichever store keeps the crinkliest plastic bags. And who insisted on repeatedly jarring the back of my chair.
Yes, if things are crowded, parking or sitting next to someone is fine and expected… but if you can very easily leave a buffer space so as to minimize the annoyance you inflict on someone, DO it!