I had to deal with the co-worker who was very sensitive and very impatient with rude customers. Instead of telling my manager about it, I took the initiative into giving her advice, which was, what comes from their attitude has nothing to do with you and has more to do with the way they handled their issues. If the situation is not going to matter in five years, then it shouldn't matter more than five seconds. And she easily accepted that advice and did not have any further problems after that.