Standardized narratives or profiles can facilitate identification of poor professional behaviour of medical students. If unprofessional behaviour is identified, educators can help the student to improve their professional performance. In an earlier study, based on opinions of frontline teachers from one institution, the authors identified three profiles of medical students’ unprofessional behaviour: (1) Poor reliability, (2) Poor reliability and poor insight, and (3) Poor reliability, poor insight and poor adaptability. The distinguishing variable was Capacity for self-reflection and adaptability. The current study used Nominal Group Technique and thematic analysis to refine these findings by synthesizing experts’ opinions from different medical schools, aiming to develop a model of unprofessional behaviour profiles in medical students. Thirty-one experienced faculty, purposively sampled for knowledge and experience in teaching and evaluation of professionalism, participated in five meetings at five medical schools in the Netherlands. In each group, participants generated ideas, discussed them, and independently ranked these ideas by allocating points to them. Experts suggested ten different ideas, from which the top 3 received 60% of all ranking points: (1) Reflectiveness and adaptability are two distinct distinguishing variables (25%), (2) The term reliability is too narrow to describe unprofessional behaviour (22%), and (3) Profiles are dynamic over time (12%). Incorporating these ideas yielded a model consisting of four profiles of medical students’ unprofessional behaviour (accidental behaviour, struggling behaviour, gaming-the-system behaviour and disavowing behaviour) and two distinguishing variables (reflectiveness and adaptability). The findings could advance educators’ insight into students’ unprofessional behaviour, and provide information for future research on professionalism remediation.