The library patron is always right - or not - or

I came across a couple of tweets from a librarian who had an uncomfortable interaction with a patron at a large academic library. The patron wondered why the library didn't have any books by Terry Pratchett. The patron asked if the librarian read Terry Pratchett. When the librarian said no, the patron said "tut-tut" (and probably a few more things - but it was a tweet, right?) The librarian's reaction was that the patron was a jerk. Well, yes, patrons can be jerks. But I wonder....what about expressing interest in Pratchett's work? "No, I haven't read his work. I'll have to put him on my list. What work of his would you start with?" What about explaining the library's collection development policy? What about suggesting other libraries in the area that might have Terry Pratchett books? Sometimes it's difficult to think of the best way to respond in the moment, but maybe the interaction could have turned into a positive one(?)