<p>In an era of viral misinformation and pervasive truth-indifferent communication, understanding what shapes everyday beliefs about what is true has never been more consequential. Little is known about the consequences of Frankfurtian bullshit (i.e., communications with little to no regard for truth, evidence, or established knowledge). A potential consequence of Frankfurtian bullshit is a deleterious effect on what people perceive to be true. Three experiments test the <i>insidious bullshit hypotheses</i> (i.e., bullshitting is evaluated less negatively, but has more negative consequences, than lying) in light of an illusory truth effect (i.e., repeated, false statements are easier to mentally process, and subsequently perceived as more truthful, than new statements). Experiment 1 (<i>N</i> = 204) analyses revealed that statements from an alleged bullshitter or average person are perceived as equally true, and more true than the very same statements made by a liar. Experiment 2 (<i>N</i> = 293) and Experiment 3 (<i>N</i> = 318) revealed bullshitters reliably produce a more extreme illusory truth effect than do objective/honest communicators and liars. Together, these findings suggest that truth-indifferent communication may pose a greater and more insidious threat to public belief than deliberate deception—not because bullshitters intend to mislead, but precisely because they do not.</p>