@pelagikat it's an in joke from Terry Pratchett books. One of the side characters is a librarian who very early in the series is turned into an Orangutan.
He very famously does NOT like being called a monkey (being bounced off the cobbles by your ears may offend) and thus the in book reference for Ape Shit is librarian poo.
@purserj Oh right! That makes much more sense! (I am familiar with Discworld but haven't read them for a while).