Correctional institutions such as youth detention centres are highly emotional places, yet there are only a few studies of youth in locked institutions that take emotions as their starting point, and those who do primarily focus on explosive affects. Drawing on video ethnographic data from a Swedish youth detention home, this study highlights a mild form of joking, what we call ‘banal humour’, employed by staff and youth as a form of affective practice. Grounded in critical humour studies and affect theory, the paper demonstrates how banal humour contributes to maintaining positive affects, and to mitigate both anger and embarrassment, while simultaneously constructing social order and producing desirable subjectivities in the detention centre.