Business Woes

As many people in business, I'm having troubles dealing with OTHER PEOPLE. How do you folks out there dealing with the mass public manage the pretentious, the two-faced, the greedy, the whiny customer? I'm usually so optimistic about things in general, but then I run across these types of people and it's like a slap in the side of the head. It really gets me down.
I have to learn to take it all in stride, I guess. Any tips?