The contradiction emerging between the lived experience of a minority of marginalised urban youth and the punitive operant conditioning of antisocial behaviour legislation is illustrative of the increasing gap between society's expectations of behaviour and the coming reality. In this paper, Loic Wacquant's sociology of advanced marginality is combined with Norbert Elias' concept of civilising and decivilising processes and applied to the dilemma of young offenders in a typical UK city. It identifies increasing educational exclusion and institutional abandonment in affected "neighbourhoods of relegation". This process is part of a general trend towards the desocialisation of labour, which ushers in a reactionary, violent decivilising process among the minority most affected, where use of violence becomes the foundation of repute for otherwise powerless individuals, or for gangs in their control of small urban spaces. By analysing this dilemma from the perspective of the "perpetrators" rather than the victims of knife crime, we seek to describe their praxis; that is, the nature of their habitus or consciousness. (Contains 10 notes.)