Recently, customer aggressive behavior occurring in service organizations, so-called "gapjil behavior," has become a social issue. Customer aggressive behavior not only leads to decreased job performance by reducing workers' motivation, but can also cause significant financial losses to organizations by triggering workers' unethical behavior. Nevertheless, companies are still only interested in how workers and organizations can influence customer satisfaction, while research illuminating how customers—particularly those who exhibit aggressive behavior toward workers—can affect worker and organizational performance remains insufficient. In this vein, this study examined the effects of workers' perceived customer aggressive behavior and psychological ownership on workers' deviant behavior within organizations (organizational deviance and interpersonal deviance), and sought to determine what moderating role psychological ownership plays in these relationships. The study sample consisted of workers in primary and secondary financial institutions and financial call center service workers, where interactions with customers occur frequently, and surveys were conducted among them. A total of 394 questionnaires were utilized for hypothesis testing analysis, and the moderation effect verification method through Ping's structural equation model was employed. The analysis results showed that as workers' perceived customer aggressive behavior increased, organizational deviance increased, and psychological ownership was confirmed to decrease both organizational and interpersonal deviance. Examining the moderating effect of psychological ownership, the moderation effect was found to be significant only for the relationship between customer aggressive behavior and interpersonal deviance. Specifically, individuals with high levels of psychological ownership showed a steeper increase in interpersonal deviance as they experienced more customer aggressive behavior compared to those with low psychological ownership. These results suggest that organizations should no longer overlook customers' inappropriate behaviors under the pretext of "the customer" but should establish selective customer response policies for effective organizational performance and human resource management. Furthermore, it should be noted that psychological ownership can have a "double-edged sword" effect: while it can have positive effects on the organization, it may also have negative effects depending on the situation workers face (customer aggressive behavior). Therefore, it is believed that organizational managers can develop into more effective and ethical enterprises by taking the lead in protecting workers' human rights as well as improving worker productivity through more proactive internal system reform.