Before I was a librarian, I was a circulation clerk. I just remembered the following conversation with a patron:
Me: You have a fine on your card of $x.xx. Would you like to take care of that today?
Lady: Really? What was that for?
Me: Um... *checks* Stop Procrastinating Now.
Both: *look at each other*
Lady: *starts laughing*
Me: I'm glad you laughed first!