Using an experimental experience sampling design, we investigate how witnessing morning rudeness influences workers’ subsequent perceptions and behaviors throughout the workday. We posit that a single exposure to rudeness in the morning can contaminate employees’ perceptions of subsequent social interactions leading them to perceive greater workplace rudeness throughout their workday. We expect that these contaminated perceptions will have important ramifications for employees’ work behaviors. In a 10-day study of 81 professional and managerial employees, we find that witnessed morning rudeness leads to greater perceptions of workplace rudeness throughout the workday and that those perceptions, in turn, predict lower task performance and goal progress and greater interaction avoidance and psychological withdrawal. We also find that the contaminating effect of morning rudeness depends on core self-evaluations (CSE)—employees high (vs. low) in CSE are affected less by exposure to morning rudeness. We discuss implications for practice and theory.