Joshikousei to Seishokusha-san summary:

There are many students at Iojaku Private Girls School who have eccentric personalities. From the girl who is overly attentive to matters regarding public morals to the point she would kneel and stare straight into the crotch of a man who is pants down on the toilet, to the delusional girl who loves her teacher way too much and often has lewd daydreams about him in school, as well as the girl who's a self-proclaimed sadist. Then there's the teacher who watches over them, an iron wall that remains unperturbed by the perverted happenings around him. (Source: Mangaupdates)