Science of a coffee cup: A physicist walks into a bar…

… and annoys everyone with unsolicited experiments. The present paper proposes a short pedagogical review of the various phenomena that can be observed in a coffee cup with little to no equipment. The physical domains spanned include acoustics, optics, and, of course, fluid mechanics. The variety of experimental and theoretical techniques introduced throughout the paper makes it suitable for a broad audience. For each topic, we first propose an experimental realization before introducing a minimal model to explain the observations. We conclude each section with a discussion of more advanced work in the literature and related applications. We provide detailed experimental procedures and videos of the experiments, which can be freely used for teaching purposes. The phenomena presented here also show remarkable efficiency as ice-breakers for morning coffee in laboratories or at conferences.