Street harassment is a widespread urban experience—particularly but not exclusively for women—yet marked by isolation from bystanders and other victim-survivors. Given this isolated dimension, what might a collective response look like? This paper examines a successful case of feminist street art protest in Brussels: posters claiming “laisse les filles tranquilles,” a demand which was swiftly extended on behalf of other groups by similar posters, and copied, commented, and modified both approvingly and disapprovingly by graffiti. Developing a novel critical phenomenological approach based in Sartre’s concept of seriality, this paper argues that the posters’ ingenuity lies in appropriating the infrastructure where harassment occurs, thus exploiting the spatially and temporally dispersed character of these intrusions. This article proceeds in three parts. First, drawing on empirical research on street harassment, I contextualize feminist protest and individual coping strategies within the postcolonial metropole of Brussels. Secondly, I reconceptualize street harassment through Sartrean seriality, combined with phenomenological insights from Beauvoir and Fanon, to underscore the dynamic between material objects, object-like social routines, and anonymity. Thirdly, I show that posters and their responses enable the formation of social antagonism between strangers who are not in a direct, physical relation, thereby politicizing the broader Brussels public.