This paper combines experimental and field data to examine how those with discretion over punishment respond when confronted with social norms of leniency. Specifically, we test how individuals who have a responsibility to punish transgressions behave when confronted with the social norm of preferential treatment on people's birthdays. We first establish the existence of this social norm using a scenario study. We then show that individuals behave in the opposite way than that suggested by the social norm: they punish transgressors more severely on their birthdays, both in the realm of actual drunk driving enforcement and in an experimental lab setting where participants were given the responsibility to punish. An additional experiment provides evidence that this effect is driven by psychological reactance rather than by overcompensation for potential bias. We discuss both the theoretical and practical implications of our findings.