Keeping your cool may be really challenging when you’re dealing with an extremely rude customer but it’s the most advisable thing to do in the situation. It is a generic advice, but it will always hold true. Rude customers are the toughest part of a customer service job but with the right mental attitude, communication, and thick skin, hopefully they’ll understand that they should not be leashing out their frustrations on you.
Assess the situation and say something like, “I understand why you’re upset,” and “I apologize for the inconvenience. Let me see what we can do to take care of the issue.” Let them know that they’re being heard and that their problem is being resolved.