How is one's reaction to a fellow ingroup member's normative hypocrisy affected by the presence of a third party observer who is an ingroup member or an outgroup member? To investigate this question we experimentally manipulated the group membership and reaction of a third party to ingroup hypocrisy in a 2 × 2 design (N = 78) and measured participants’ personal endorsement of pro-environmental attitudes and behaviors that were normative of the ingroup. As predicted from a social identity analysis of the function of norms and prototypes in social influence processes, personal endorsement of pro-environmental attitudes and behaviors was strongest when an outgroup member remarked negatively on the hypocrisy, and weakest when an outgroup member did not appear to notice the hypocrisy. We would like to extend our gratitude to Christopher Aberson and the psychology department at Humboldt State University where these data were collected. In addition we thank our actors, Jacob Crummey, Kimberly Altic, and Katrin Beene, for their contribution to this project. Finally we would like to thank the reviewers who contributed their expertise and insight to this work.