Libraries are not necessarily pleasant places to work. I spent the first four years on the service desk scared witless. I kept thinking, “Are they kidding, does stuff like this really go on in a library.” YES! From the mentally ill, to the homeless, to the smelly, to the rude and socially inept, the answer is yes.
Of course, the majority of patrons are very nice. But, librarians do get killed,—a past library directory of my library was murdered in the library!—and patrons do go postal. Take the 2010 University of Texas incident in which a student opened fire in a the library with an AK-47 and then killed himself. You might want to make sure your library has a good emergency plan.