When you think of back-to-school season, these aren't the types of relationships that come to mind. At what point does it become acceptable for a student to date a teacher? It's obviously a no-no if the student is underage, but some colleges have banned student-teacher sex completely, even between consenting adults. For years, the topic has fascinated filmmakers far beyond the made-for-TV movie about Mary Kay Letourneau. In fact, a particularily racy take on these these scandals is out today, the film A Teacher. Here are student-teacher liaisons that cross the line from cute to questionable.