This study aimed to ascertain how the four domains of self-debasing cognitive distortion, namely personalisation, catastrophising, overgeneralisation and selective abstraction, could predict or inform emotional disturbance in the reactions of bystanders when witnessing bullying behaviour. We utilised purposive sampling to select 10 bystanders of school bullying for participation in the study and performed convenient sampling to select a research site. We conducted interviews that were recorded on a voice recorder and transcribed thereafter. Qualitative data was analysed through inductive thematic analysis. Our findings revealed that personalisation evoked bystanders' self-blame and feelings of guilt, catastrophising amplified their anxiety and fear, overgeneralisation induced and exacerbated their negative perception of school safety, and selective abstraction led to indirect co-victimisation. Based on our findings, we recommend that school psychologists, counsellors 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.