This paper explores the impact of social preferences, specifically through Social Value Orientation (SVO), on responsible consumer behaviour and sustainable decision-making. We adopt a behavioural economics perspective to develop and empirically test a model that connects prosocial preferences with environmentally responsible choices, particularly in private cost–public benefit situations. Our experimental task, the Green Game, assesses consumer trade-offs across three treatment conditions: control, norm-based nudge, and eco-label. The findings reveal that individuals with higher SVO scores consistently favour green options and show better responsiveness to social norm cues, even when facing higher personal costs. Conversely, participants with lower SVO scores tend to opt for default choices when cost disparities are significant. Regression analysis indicates a notable interaction between prosocial orientation and nudging strategies, especially in the presence of normative cues. These results highlight that customised behavioural interventions that align with individuals’ internal motivations can promote sustainable consumption. The Green Game illustrates how experimental economics offers valuable insights for policymakers, assisting governments, municipalities, and the private sector in encouraging environmentally benign consumption practices through soft regulations. This research contributes to theory and practical applications by elucidating the interaction between psychological traits and behavioural framing for effective environmental policy design.