How are individuals affected by their own self-interested unethical behavior? Although self-interested unethical behavior commonly occurs as people attempt to advantage themselves, we argue that this unethical behavior can have deleterious implications for individuals and their social relationships. We propose that engaging in self-interested unethical behavior is positively related to state paranoia—an aversive psychological state. In turn, the social cognitive biases underlying state paranoia can prompt people to misjudge the potential for social threat. This may motivate them to curtail coworker-directed (...) affiliative behavior, thereby inadvertently undermining their social relationships. Our predictions were supported across four studies, including a behavioral study in a controlled environment, a recall study, a field survey in a single organization, and a two-wave survey. Theoretical and practical implications include highlighting the importance of understanding the personal and social consequences of self-interested unethical behavior as well as the impact of state paranoia in the workplace. (shrink)