A book called "Hush" by Anne Frasier. I finished it but it was a struggle.

While studying French at college I once voluntarily read "Madame Bovary". I lasted about 50 pages.

But the shortest read was (although it was a book on our college course) L'Etre et Le Neant (Being and Nothingness) by Jean Paul Sartre. I got three quarters of the way down the second page before tossing it aside.