An ex post analysis shows that avoidance, as against associating, by smoker and non-smoker when the former smokes is a Nash outcome. Ex ante, passive smoking occurs because socio-legal structures allow smokers to take non-smokers for granted. This can be done away with if smoker’s cost (material plus non-material) of associating with a nonsmoker while smoking is greater than that of avoiding. To ensure this, norms and conventions of avoidance ought to be developed and the health-risk of passive smoking should be made common knowledge. As a special case, a single person’s active smoking behaviour has also been analysed.