Guided by assumptions from the cognitive-affective theory of learning with media, we conducted a teaching experiment to corroborate past correlational research that suggested instructor misbehaviors, in the form of antagonism toward students, impede students' cognitive learning. Participants were 472 undergraduate students who were randomly assigned to view a recorded teaching condition of a standard lecture on persuasion heuristics (control), or the same lecture content with instructor antagonism manipulated (treatment). Results revealed that students exposed to the treatment lecture with antagonism had lower affect for the course and instructor. Moreover, because they had lower affect for the material, antagonized students scored worse on a test of their learning (mediation) compared with students in the standard lecture. Students who possessed a mastery orientation toward learning, and independently, who were effort-regulated, scored even lower on their tests of learning because antagonistic instruction caused a greater reduction in their affect toward the material being taught (moderated mediation). Overall, results suggested that instructor misbehaviors do cause slight learning deficits for students, especially for students who value their learning opportunities.