A marked feature of the political tactics of the transnational School Strike 4 Climate movement (also known as Fridays for Futures and Youth Strike for Climate) has been the use of humour on cardboard signs, digital memes and social media posts. Young people's cardboard signs, memes and social media posts have frequently mobilised humour as public pedagogy and political intervention -- to emotionally stir and to politically engage others. In this article, we argue that the school strikers' creation and mobilisation of humour demonstrate a "critical affective climate justice literacy" that educators committed to pursuing climate justice have much to learn from. In analysing examples of humour in contemporary student climate justice activism, this article brings previous analyses of the potential of humour in social movement studies and climate change communication into conversation with calls from environmental education scholars to pay greater attention to the potency of emotion for climate justice education, beyond a rationalistic focus on climate science literacy. We outline four pedagogical propositions for working with humour, accompanied by their own perplexities, in moving towards critical affective climate justice literacies.