A person who is so anal that they have sought a job to define their compulsive tendencies. As librarians, these 'overly enthusiastic' individuals can not only revel in their compulvieness, they can force it on other people too. Librarians often bait people into their dens by offering information or entertainment, usually of the wholesome kind.
Information in Librarian dens (often called Libraries) is sorted meticulously by a variety of nonsensical systems. Some libaries have been known to assign numbers to CDs in the order they purchase them and then organize them by number, effectively hindering any person from finding the CD that they want.