Technically, no one is required to take any of the courses I teach (at either the undergraduate or graduate level).
There is a political theory requirement for undergraduate political science majors, but it’s only one course and it can thus be fulfilled by taking the introductory course (which is taught by one of my graduate students) rather than one of my upper-level courses.
For the past six years, undergrads in political science at the University of Nebraska who wanted to make political theory one of their three subfields of study would have to take at least one course with me because the subfield requirement called for at least two courses. This won’t be the case any longer, as my department voted to eliminate political theory as one of the subfields of undergraduate study last semester. My suspicion is that, over time, the number of students in my courses will dwindle as more and more students simply elect take the intro course and steer clear of the upper-level courses (less because of my grading practices and more because they don’t fulfill any sort of degree requirement).
There might still be one or two students who choose to take all of the classes I offer. In his or her final semester, I might buy a weekly doughnut for such a student.