Why do some people try purposefully to get you, make your life tougher, etc?

Don't allow them to get the best of you. Just remember that if that bank teller got out of line then he would have been fired or disciplined. You are just trying to live your life, and it is his job to provide you with service. Furthermore, just because the bank teller might be miserable in his job it doesn't necessarily mean that it due to your appearance; he likely wasn't mad at you.