Dealing with an irate person

Open Loops has a good tip in how to deal with irate people: "Pace and Lead".  The "Pace" part is initially matching the emotional intensity of the person, then gradually toning your comments to a more normal level.  If the person with the problem sees the listener reacting in the same way as they are, they feel better heard and understood, whereas if the listener was calm all the way through, they would have given the impression that they were not understood, which only increases the frustration and anger.