This chapter analyses the relationship between loneliness and antagonistic political emotions. Loneliness is commonly defined as a painful experience resulting from a discrepancy between desired and actual relationships. Philosophical literature highlights its impact on self-perception, agency and possibilities for connection, yet its political dimensions remain largely overlooked. To address this gap, I examine the case of a lone-actor terrorist whose loneliness motivates a search for meaning within a radicalised community. In this context, loneliness combines with emotions such as vengeful anger and envy. This raises key philosophical questions: How should loneliness be understood? Can it count as a political emotion on its own or only when coupled with other affective states? How does loneliness interact with antagonistic emotions? I call hostile loneliness the affective state in which loneliness conditions the emergence of aggressive and oppositional emotions. These emotions enable lonely individuals to reclaim agency and pursue radical social and political change. They become fully political when taken up collectively and expressed by a community.