Although people buy counterfeit products to signal positive traits, we show that wearing counterfeit products makes individuals feel less authentic and increases their likelihood of both behaving dishonestly and judging others as unethical. In four experiments, participants wore purportedly fake or authentically branded sunglasses. Those wearing fake sunglasses cheated more across multiple tasks than did participants wearing authentic sunglasses, both when they believed they had a preference for counterfeits (Experiment 1a) and when they were randomly assigned to wear them (Experiment 1b). Experiment 2 shows that the effects of wearing counterfeit sunglasses extend beyond the self, influencing judgments of other people's unethical behavior. Experiment 3 demonstrates that the feelings of inauthenticity that wearing fake products engenders-what we term the counterfeit self-mediate the impact of counterfeits on unethical behavior. Finally, we show that people do not predict the impact of counterfeits on ethicality; thus, the costs of counterfeits are deceptive.