I'm usually 'the finisher' when we've got a customer that's being an asshole. It's good
One of the things my department's responsible for is maintaining the sales tax exemption certificates for customers. The laws are stupidly complex, so customers will pretty regularly screw up during the process of getting a certificate together. Some of the shit is pretty basic...forgetting to fill out any of the spaces (what they're going to buy, what it is they're going to do) - annoying, not a big deal. Most of the time, I just let the small details go (the state doesn't really pay attention to the certificates, anyways) in order to be convenient to them. Every so often, though, we'll get someone trying to give us an egregiously incorrect certificate or something like that - and when one of the women in the department tries to explain the mistake to the customer, the customer will go off on them, saying that they don't know what we're doing, etc.
That's where I step in...and spend 10 minutes trying to say, in a nice way, "no one else has ever come back to you about this because no one else understands this state's retarded sales tax laws" or "your accountant said the certificate was okay because your accountant is a slack-jawed idiot". Most of these guys just need to hear an authoritative sounding voice. I've had a couple of situations where the customer's come back at me, though, and I've gotten involved in shouting matches, a lot of "look, I'm not going to transfer you to anyone else, I make the decisions about this, so this is where this conversation is going to end", one time where I spent 30 minutes on the phone with some guy not saying anything, just listening to each other breathe, shit like that. It's fun.
STUN!