Some people are very mean to their fellow men. Sometimes you can't change that. However I do know that when you approach people in a nice manner, you will get much better results.
Politeness is always welcome, and people should do that more often nowadays. We need to work on getting back those morals that used to exist 100 years ago.
-OR- Because your too concerned with what people are thinking about you which leads to you becoming a tool which no one likes.