Self-affirmation interventions can reduce defensive responses to threats to the self, but have had limited reach to the general population. We sought to create an effective and feasible version of the Kindness Questionnaire self-affirmation intervention for use on a mobile device outside the traditional university laboratory setting and by non-student participants. In an online experiment, 603 cigarette smokers (M-age= 37.5 years, SD = 10.2) were randomly assigned to one of six conditions in a 2 (Self-Affirmation: Self-Affirmation, No Self-Affirmation Control) x 3 (Example Type: Written, Imagined, No Examples) fully-crossed design. Participants read a message about the health harms of smoking. None of the self-affirmation variations were effective or feasible: the self-affirmation showed null effects on the primary outcomes of message acceptance, perceived message effectiveness, and reactance. It also backfired by reducing intentions to quit smoking and risk perceptions. Participants spent little time reading the health message, and those in the written self-affirmation condition infrequently provided detailed responses. Translating interventions developed and tested for efficacy in laboratory settings to real-world settings is necessary but challenging.