The Chile uprisings in late 2019 and early 2020 saw protests on a scale unprecedented in its democratic era, with citizens taking to the streets and social media to express their grievances, centred on vast inequalities and injustices inherent to the neoliberal Chilean state. They did so through creative performance and the deployment of objects and symbols that came to signify and embody their struggle. Among these was the black flag, an appropriated version of the Chilean national flag. We use this provocative object to show how flags can be deployed by national citizenries to generate certain affective atmospheres of shame, mourning and despair directed at the nation. Furthermore, we show how citizens were actively involved in designing and making flags that expressed their feelings about the nation - a process that was, at times, cathartic, and which also involved reimagining the Chilean nation. Scholars of everyday nationalism have emphasised the individual agencies of national citizens, the materialities of objects like national flags and the atmospheres that can emanate from them, yet this existing research has placed less attention on the collective, subversive interventions of citizens that attempt to (re)define and (re)think the nation. Conversely, alter-geopolitics (Koopman, 2011) has explicitly encouraged political geographers to draw attention to grassroots interventions that bring bodies together to resist state (in)security and build alternative non-violent securities. We argue, then, that everyday nationalism's sensitivity to agency, bodies (both human and non-human) and affective national atmospheres can be brought into productive dialogue with alter-geopolitics, to underline the political potentialities of national flags and the ways they can be collectively engaged by national citizenries. National flags can be (re)appropriated from the ground up, by citizens, in ways that invest them with potential to critique, provoke and protest against the 'nation-state'. They can also do much more than this, putting forward alternative visions and imaginations of the nation, as well as reanimating ideas about national citizenship and political participation.