Student Bodies (1981)

In this seminal horror-comedy, an anonymous killer known only as "the Breather" (Richard Brando) terrorizes the teenagers of Lamab High by killing every student who indulges in sex. The long list of suspects includes the school's psychoanalyst (Carl Jacobs), nurse (Janice E. O'Malley), principal (Joe Talarowski) and, most surprisingly, virginal student Toby (Kristen Riter), who's always at the scene of the crime. Toby knows she's innocent, however, and vows to catch the killer.