Conflict management, always a troublesome matter.
Stay calm and polite at all times. People who are being rude, probably have had problems. Ask what the problems are, and see if you can do anything about it.
If they're just rude for no reason, just refuse help them. Client is king, but that doesn't mean you're not as valuable. If they can't handle things politely, you should just refuse to help them any further. Might not be the best solution, but you don't want your company to be subassertive, otherwise many others will just run over you.