Focusing on a Hong Kong online discussion involving ‘Jenny’, who was later described as the ‘Kong Girl’ prototype, this paper demonstrates a method to study gender stereotype as both semiotically and discursively constructed. It traces the perceivable signs in online posts as demeanor indexicals (Goffman 1956, Agha 2007), and discusses how forum participants collectively develop Jenny’s public persona as a woman who is materialistic and has an entitlement attitude, qualities that later become emblematic of the Kong Girl stereotype. This analysis proposes a framework for how interpretive discourses mediate between the situated social media context and gender ideologies, and contributes to an understanding of the role of demeanor indexicals in the construction of a stereotype that is not associated with a linguistic register. It provides insights into local gender dynamics and illustrates how a private dispute becomes entangled in a public consensus building process that is necessarily selective, emergent, and positioned.