My 13 year old son has a very self centered attitude about him. Everything is for his benefit only and he never considers other people's feelings. He is always demanding things of me, such as "where is dinner" or "get this for me". Whenever I decide to take him and his sister (10) to a movie, I ask which one they would like to see. Of course they never agree on one, which means I have to choose, and I usually take turns for whom I choose each time. But if it is not the one he wants to see, he starts making negative comments about how stupid the other movie is and goes on and on about it. He does the same if we choose to go out to eat and a place that he doesn't like. Whenever his sister is telling about something he will also say negative things about her comments, whether he knows what she is talking about or not, just to argue with her.
Is there something I can do to encourage him to not be so negative or to think about others?