© 2021, Emerald Publishing Limited.Purpose: The present work attempts to investigate how restaurant staff perceive problematic customer behaviours (PCBs), the causes for PCBs and the core reasons that trigger such behaviour in restaurants. Design/methodology/approach: The root causes were determined by systematic grading and then aggregated in a fishbone diagram to illustrate the real antecedents. First, the data obtained from in-depth interviews based on the grounded theory approach, conducted with 29 frontline employees in restaurants, were categorised using open, axial and selective coding. Then the 26 causes identified were graded and arranged into six levels, forming a chained hierarchy for each behaviour. Findings: Ego-derived faults are among the key factors stemming from the personality of the customer, and the use of money as power is evident in such behaviours. In terms of issues related to social systems, the main factors were the structure of the sector, the “customer is always right” philosophy, other factors resulting from the local culture and the occupational image. Research limitations/implications: First, more frequent and effective addressing of the sector structure can help employees feel more comfortable. Second, the study uncovers emotional and psychological aspects as core factors causing PCBs, paving the way for future studies. Practical implications: To prevent PCBs, it may be necessary to provide relevant training for employees, empower leadership for middle-level managers and set up a customer crediting system as well as a customer blacklist based on smart technologies. Originality/value: This research is the first attempt to reveal the root causes of the factors behind PCBs by forming graded-reason chains and representing integrated PCBs in a fishbone diagram. Using this instrument, the paper investigates the insights of employees to address a topic that few studies have dealt with thus far.