In this study we offer a socio-pragmatic examination of instances of what is generally known in social psychology as "bystander intervention," i.e., the social action by which a bystander steps in and attempts to prevent a wrongdoer from abusing a victim. We explore the relationship between (im)politeness and participants' perceptions and understandings of moral principles as evidenced by their metacommunicative voicing. Our analysis concentrates on cases of bystander intervention in the US by analyzing data drawn from a reality show. Bystander intervention is a noteworthy phenomenon to examine for, at least, two reasons. First, it is a type of aggressive social action as it poses an uninvited and open challenge to the wrongdoer in public. Second, bystander intervention challenges conventional behavioural norms. It aims to reinstate what the intervener regards as morally appropriate behaviour. This study aims to contribute to current research on (im)politeness by offering a yet unexplored dimension: that of the interface between metapragmatics, (im)politeness and (im)morality in the interactional arena of bystander intervention.