As someone who's worked in custoemr service for about 12 years now, I'm often the guy who will stick up for myself. The customer is not always right and I refused to be treated like the scum of the earth because you're having a bad day.
I was the person that all the angry people got sent to, because I have the uncanny ability to never be angry. If the customer wants to rant and rave and yell, and demand this or that, I would politely and professionally inform them what we can and can't do, as many times as they cared to make me repeat myself, all while keeping the same calm attitude.
It -really- pissed them off. It was great.