What is the worst experience you've had reading a book?

Perhaps a hot take, but East of Eden was an absolute trudge to get through. I think I made it almost halfway and gave up because I was not enjoying it at all. I wasn't sure what the main points were and there were too many details unrelated to the plot.

A less hot take, The Fountainhead was also a pain to read. It was just boring as hell and I stopped about halfway as well. I only read it because I loved Anthem and became disappointed to find out it's only related philosophically.