Peer conversation provides an important platform for people to explore and disseminate sexual health knowledge. Humour forms part of conversations held between peers including those where sexual health and sexual decisions are discussed. The central argument of this article links conversation, humour and peer education. Drawing on interviews and diaries kept by 12 student peer educators over a two-month period in a South African university, the article explores the forms and functions of humour in instigating and encouraging informal peer education between young people in a university setting. The evidence shows that humour can foster intimacy, familiarity and camaraderie in peer interactions; keeps conversation moving; and acts as a gateway to discussion of taboo, personal and private subjects that lie at the core of effective peer education. Components of humour (joking, teasing, innuendo, provocation) and the transformation of the serious (and boring) into the enjoyable (and accessible) are found in these peer interactions. However, humour can also limit communication by keeping conversations light and superficial or, in the case of inappropriate humour, close conversation altogether. Acknowledging the nuances of humour within conversation and peer education allows for a clearer understanding of the ways in which humour contributes to effective health promotion efforts and how it can be used within peer educator practice. The effect of the personality traits of peer educators on effective use of humour in conversation is an area that could benefit from further insight and research.