Taxi zum Klo (1981)

Frank Ripploh is a bit of a rascal: he's a bearded and shaggy-haired teacher, and he's gay with a very active sex life and an interest in making films. He keeps his personal life and teaching separate, but he sometimes corrects student papers in public toilets as he waits to score. He cruises constantly, and one evening, he meets Bernd. They become lovers. While Bernd is attentive and caring, Frank gets bored and continues his polymorphously perverse ways. For how long will Bernd and Frank tolerate each other's habits, and for how long can Frank keep his sexual orientation out of the classroom? Things come to a head during Berlin's annual Queen's Ball and the morning after.

Source: TMDb