Gorby - this is not at all uncommon. Handling live calls is like being on stage, and it can be a bit nerve-wracking. One of the greatest stage actors ever, Lionel Barrymore, said that there was never a performance where he did not feel nervous going on.
The trick is to master that nervousness in some acceptable way. Picturing the client naked? Hmmm... I don't know about that one. I guess depending on your customer base, that could be interesting.
I would suggest more tactical things, like taking several really deep breaths before taking the call. Or, once on the call, getting in some brief small talk with the customer, especially if some humor is involved. Laughter is a great tonic for nervousness.
The other thing to stress to your rep is that the customer, even if he is angry, is coming to her for help. She is the key to helping him get what he wants or needs. By actually articulating to the customer, "I can help you with that," one gives assurance to oneself, as well as the customer.
Finally, if there is fear of being harassed by an angry customer, let your rep know that angry customers are a great source for business improvement, and if you can get past their anger (which is usually not directed at the rep personally), you can discover ways of improving your business processes or products or services. Role-playing in training is a good way to "toughen up" reps who get nervous around customers.