Most existing researches explore the influence mechanism of workplace incivility from the perspective of target, ignoring the roles and behaviors of observers as the third-party force in workplace incivility. This study provides a new direction for the theoretical study of workplace incivility from the perspective of observer. In this study, we propose a moderated mediation model to clarify the double edged sword mechanism of coworker incivility on observer behavior, and tested it using three-wave data from a sample of 467 supervisor-subordinate dyads in mainland China. We found that coworker incivility urges observer to implement negative gossip by enhancing schadenfreude, or to perform helping behavior by enhancing other-suffering moral emotion. However, whether observers take negative gossip or helping behavior depends on gender similarity with target. Coworker incivility can better promote observers to implement negative gossip when the observer and target have different genders. Our findings provide novel insights into how and why observers take different behaviors facing coworker incivility.