This article reports upon research on vegan transition, which I bring into dialogue with Sara Ahmed’s figure of the killjoy. Ahmed’s work on affect and the feminist killjoy is found to be apt for considering contemporary vegans and their transgression of normative scripts of happiness and commensality in a dominant meat and dairy consuming culture. The decentring of joy and happiness is also found to be integral to the critical deconstructive work of the vegan killjoy. Ahmed’s ideas further complement the frame of practice theory that I draw upon to understand the process of transition especially in the sense of opposing the meanings of dominant practices. Although food and veganism are not commented upon by Ahmed, the vegan subject constitutes, I argue, a potent further example of what she terms an “affect alien” who must willfully struggle against a dominant affective order and community. Drawing upon interviews with 40 vegans based in the UK, I illustrate examples of contestation and negotiation by vegans and those close to them. The article finds in the figure of the killjoy not only a frame by which to partly understand the negotiation of relationships between vegans and non-vegans but also an opportunity for further intersectional labour between veganism and feminism.