The purpose of this study is to ascertain how the four domains of self-debasing cognitive distortions, namely personalisation, catastrophising, overgeneralisation and selective abstraction could predict or inform bullying bystanders' emotional disturbance in reactions to witnessing bullying. A descriptive case study research design was adopted. Ten school bullying bystanders were purposefully selected to participate in the study. Interviews were recorded on a voice recorder and then transcribed. Qualitative data were analysed through inductive thematic analysis. The findings of this study revealed that personalisation evoked bystanders' self-blame and feelings of guilt, catastrophising amplified bystanders' anxiety and fear over generalisation-induced and exacerbated bystanders' negative perceptions of school safety, and selective abstraction led to indirect co-victimisation. It is recommended that school psychologist, councilors and behavioural healthcare service providers should teach victims of bullying, especially bystanders, how to recognise, challenge and reappraise negative and unhelpful thoughts and feelings related to their experiences.