This article presents an investigation of the use of social categories in talk about Christians in a small community of users discussing religious issues on the popular video-sharing site, YouTube. The article focuses on how self-proclaimed atheists employed and modified the category of “Christian” to describe others in a series of antagonistic debates – called “drama” by users. Three video pages, including video talk and comments, were analyzed using membership categorization analysis (Housley and Fitzgerald 2002) to focus on how users, and in particular atheists, employed and modified the category of “Christian” to talk about others. The analysis shows the category of “Christian” was used in different ways to evaluate the actions of others, often leading to conflict about the use of the category. The study shows how the meaning of categories is dynamic in talk, and how local, specific uses emerged as stable on different timescales in the drama. Findings also show that categorization often revealed user beliefs and expectations about social interaction, particularly when the categorization led to moral judgments.