I've read quite a few of the "top best greatest of all time" books that were poorly written and dull as hell: Silas Marner, Moby Dick, the Leatherstocking Tales all come to mind. And they were required reading when I was in high school. I still suspect they were put in the curriculum to make adolescents believe reading was inherently boring. Not a whiff of Salinger, Vonnegut, Fielding, Joyce, Cabell, James, etc.
But the worst that was highly recommended...? There was a fantasy trilogy published some decades back about a modern leper who ends up sucked into another dimension, where he's always hurting everyone else, but so self-involved that we're supposed to forgive everything from constant moodiness to rape. The best thing in it is that he truly dies at the end of the third book. An example of a more self-pitying, unrealistic character just doesn't come to my mind. I don't remember the title, and that's just as well.