I couldn't get a reservation at the library. They were completely booked.

Behind the Groan

Two Ways to Be Booked

A restaurant or event is “completely booked” when every reservation has been taken. A library is also literally full of books, so the same phrase describes both its schedule and its shelves. The setup works best as a mildly surprising complaint because libraries do not normally require reservations. Pause after the first sentence, then give the explanation with complete seriousness. The familiar booking phrase supplies the practical meaning first, while the location makes the literal book meaning unavoidable a moment later.