DANGER: I used to quote HitchHiker by the quarter-hour, as Herself will attest. These days I've graduated to Discworld, but one of my favourite real-life incidents was:

When I was at Uni, my father sent me a cutting from the Grauniad, announcing that HHGthG was out in paperback. So I went to the bookshop on campus ....

Me: Do you have a copy of the HitchHiker's Guide to the Galaxy?
Assistant: I'm sorry, we don't sell travel books.

I was five yards out of the door before the penny dropped.