Social tensions impede social cohesion and public goods provision, and can be a driving force for more serious conflicts such as civil wars. Surprisingly, the emergence of social tensions has been studied only rarely in the literature. In the present contribution a game-theoretic model highlights how reputation concerns and the structure of group cleavages matter for the emergence of social tensions. In particular, the respective effects of ethnic fractionalization, polarization and segregation are analyzed. The differences between ethnicity and class, and the role of social mobility are also studied. The predictions of the model can account for recent empirical evidence.