This isn't a reference question, but it is something desk staff face on a daily basis.
The clip below comes from an episode of Family Guy from a few weeks ago - initially I cringed at negatively portraying public libraries, but then I realized just how amazingly accurate it was. The librarian could be nicer though:
I'm sure every library has its "regulars," but I was struck by how well the writers captured a typical interaction - how, no matter what, it's almost impossible for staff to extricate themselves. Now that is a skill I would love to learn.
I've asked if we could have some kind of button installed under the desk that would just make the phone ring, so we could use that as a reason to break off the aimless and never-ending conversations. No progress yet on a button, so I need to come up with other ideas.