What term describes a caller who has become angry or upset?

The term "difficult callers" is the most appropriate choice to describe a caller who has become angry or upset. This term encapsulates a range of emotions that can manifest during a telephone conversation, including anger, frustration, or dissatisfaction. In customer service and business operations, handling difficult callers effectively is crucial as they may require special attention and skill to resolve their issues and restore their trust in the service or product.

Understanding the nuances of different types of callers is important in business settings. While "exasperated clients" and "frustrated customers" do convey that the caller is upset, they are somewhat more specific and may not encompass all behaviors exhibited by someone who is difficult to engage with. Meanwhile, "challenging contacts" is a broader term that could apply to any number of circumstances beyond anger or upset, making it less precise in this context. Therefore, "difficult callers" serves as the most comprehensive and accurate label for individuals who are expressing anger or upset during a call.