I guess the answer to the question why people are mean in any kind of situation, environment, etc. is the same and was greatly put in an old (great one by the way!) movie.
" -Why are you so polite?
- for the same reason you aren't: it's the way I was brought up."

Just don't bother with people who have bad attitude. You will have to suffer few minutes with them (even less if you kick them), while they have to spend the whole life with themselves!

Regards,
M