How about this: college student (over eighteen) goes to a swing club, the type where everyone wears a mask. He (or she) meets a hot woman (or man) and has a fabulous, anonymous time. Per club rules, no discussions of names, address, profession, etc., are allowed.
But the hottie from the club seemed very familiar to the student. Back in class on monday, he realizes that the hottie was very reminiscent of a ball-busting teacher that makes his life a living hell in class. He stares at her during lecture, watching her moves, her mannerisms, trying to figure out if the teacher was the hottie from the club. He can't decide.
He has to go back to the club the next weekend, finds the same hottie, hooks up again, and tries to figure things out with clever questions, cute moves, etc.
Ending could go several ways, but it's the tension before the big reveal that makes it interesting (at least, to me). Also, although I would write it with male student and female teacher, certainly any combination of sexes of the two leads could be made to work. It might even make a good "first time gay" story with a straight male student and a male teacher/hottie.