We focus on two cases in which participants narrate and perform a new culture of expertise by constructing a bad expert, a reviled or dangerous figure of scientific credibility gone wrong. We show that a key mechanism in the construction of expertise cultures is the use of antithesis performances, which are performances of scientific and professional credibility that rely on telling stories about a scientific enemy or ostracized Other. By performing the antithesis of the bad expert, actors help generate turning points in expertise, allowing new cultures of expertise to emerge. Our two case studies are: (1) feminist therapeutic expertise related to domestic violence, and (2) the revival of psychedelic medicine. In explicating these cases, we link the jurisdictional model of expertise (from the sociology of professions) with the network model of expertise (from science and technology studies): Cultural factors such as scientific narratives and embodied performances link together expert domains and forge new boundaries around expert practice.