Towards the end of episode 4, around the 18th minute mark, the girls are discussing the title of book(that is supposedly BL). Hanako suggests Anal Bum Cover (according to the subtitles). At that point the teacher screams and asks her not to tarnish her bible.
So, is Hanako's title based on some famous Japanese book?
According to this review, the term is slightly mistranslated, and is closer to 'Please Save My Butt', a play on 'Please Save My Earth', which is the series that is garnering the reaction.
As a side note, Anal Bum Cover is most likely a reference to the Saturday Night Live skit 'Celebrity Jeopary', in which "Sean Connery" reads the category "An Album Cover" as "Anal Bum Cover"
