<p>In the workplace, employees frequently interact with their coworkers, influencing one another in various ways. However, the specific impact of coworkers’ behaviors on employees remains underexplored. Grounded in impression management theory and guided by the cultural framework of individualism–collectivism, this study proposes a moderated mediation model. Data were collected through a three-wave survey from 312 full-time employees in China. The findings indicate that coworkers’ proactive behavior triggers focal employees’ concern with maintaining a positive image in front of their peers. This concern, in turn, enhances their work effort and interpersonal citizenship behavior. Furthermore, employees’ collectivistic orientation strengthens the positive relationship between coworkers’ proactive behavior and focal employees’ proactive reputation maintenance concerns. The strength of the indirect effects of coworkers’ proactive behavior on both work effort and interpersonal citizenship behavior also varies as a function of employees’ collectivistic orientation. This study highlights the critical role of individual cultural values in shaping employee responses to coworkers’ behavior, offering new insights into the interpersonal dynamics of proactive behavior in organizational settings.</p>