The Criminal Justice Act 2003 ushered in a new system for determining the admissibility of bad character evidence in criminal proceedings. Unfortunately, this system is riddled with anomalies and plagued by obscurity. These problems contaminate its core as it is unclear what constitutes 'bad character' evidence. This uncertainty is in large part due to the fact that the Act offers little clue as to the meaning of the words 'reprehensible behaviour', evidence of which is 'bad character' evidence. Accordingly, this article asks whether the decisions in which the expression 'reprehensible behaviour' has fallen for consideration shed light on its content. It is concluded that the authorities offer scant guidance and have introduced several difficulties.