A woman comes up to the reference desk and bursts out laughing.
I look at her oddly and she says
"Oh, I'm sorry, I just thought of this joke I heard once: A blonde goes into a library and asks the librarian, 'Can I get a cheeseburger, fries and a shake?' and the librarian says, "Miss, this is a library!' And the blonde says 'Oh sorry, (whispering) can I get a cheeseburger, fries and a shake?' "