Why do some people who are fighting in a war or fought in a war think that they are better than others?

I go to a medium sized school and there are a few people who groped out to get in the army and got back in school and they think they are better than everyone. The teachers love them and let them do what they want. They get honored at all emblys and they have their picture in hallways. They steal peoples seats in the cafeteria, they are very trashy, they cuss a lot, and more.. They are just rude. Is there a reason for this? No! I'm not talking about everyone in the army. Just everyone at my school who was in the army,