This study explored frontline employees’ perceptions of and responses to illegitimate customer complaining behavior (ICCB) in hospitality business settings. In-depth interviews were conducted with frontline employees who had firsthand experiences with ICCB. Analysis of data revealed three types of illegitimate complainants as perceived by frontline employees: opportunistic plotters, repetitive grumblers, and occasional tyrants. In addition, some unique patterns of employees’ responses to ICCB were identified, including the double-whammy effect of ICCB on employees’ evaluative and emotional responses, emotional paradox, learned helplessness, and process-focused coping. Based on the results, this study developed a conceptual framework with four propositions related to frontline employees’ responses to ICCB. The theoretical and managerial implications of the findings were also discussed.