Pranking can be understood as challenging a normative social order. One environment where pranking occurs is in institutional interaction. The present study examines a sample of pranking calls to telephone helplines for children and young people. Some cases had been posted on YouTube by the person doing the pranking; others were from a subcollection of possible pranks, extracted from a larger corpus of Australian children’s counselling helpline calls. Drawing on ethnomethodology and conversation analysis we aim to understand the inferential and sequential resources involved in pranking within telephone-mediated counselling services for children and youth. Our analysis shows pranksters know the norms of counselling helplines by their practices employed for subverting them. YouTube pranksters exploit next turns of talk to retrospectively cast what the counsellor has just said as a possible challenge to the perception of the call as anormal counselling one. One practice evident in both sources was the setting up of provocative traps to break a linguistic taboo. This detailed study of pranking in interaction provides documentary evidence of its idiosyncratic yet patterned local accomplishment in telephone-mediated counselling services aimed at children and youth.