Guided by an affective theoretical process, we surveyed college students (N = 397) to examine the effect of college instructors' lecture misbehaviors on students' emotional interest directly, and indirectly through affect toward the course content, among students who varied in their desire to master the course material (i.e., first- and second-stage moderated mediation by students' mastery goal orientation). Results of a conditional process analysis revealed that students' mastery goal orientation emerged as a moderator of the negative direct and indirect effect of lecture misbehaviors on students' emotional interest. Students' emotional interest declined directly as a consequence of lecture misbehaviors, and indirectly through a loss of student affect for the content, but these effects were stronger for students with higher mastery needs. The indirect effect of lecture misbehaviors on emotional interest through reduced affect for the course content was a nonlinear function of students' mastery goal orientation. Probing of nonlinear moderated mediation revealed that students with increasing mastery goals became susceptible to an accelerating and (more) negative affective process.