How does public diplomacy shape global public opinion? In this note, we theorize that positive public diplomacy that emphasizes aid and friendship works, while negative messages that criticize international rivals are ineffective. We conduct an experiment, to our knowledge the first of its kind, that randomly exposes Indian citizens to real Twitter messages from Chinese diplomats. We find that positive messages emphasizing aid and friendship improve perceptions of China, even in times of escalating violent conflict. However, messages from so-called “Wolf Warrior” diplomats that harshly criticize the United States are ineffective and can backfire in times of crisis. We argue public diplomacy can be a useful tool for global powers, but that domestic political pressures have pushed some diplomats, like China's Wolf Warriors, toward nationalist messages that do not appeal to foreign audiences.