The Troll Whisperer
This is a fantastic essay by Cory Doctorow. I wish it were three paragraphs longer, but it lays out a thoughtful analysis of the flame/idiot/troll phenomenon.
My take: you can't (and shouldn't) treat all customers the same. It's not clear to me that you can always change the attitude of an angry person. But you can avoid bringing down everyone around them.