Of Mice and Men. When I studied it in school I hated it, because I hated how my english teachers wouldn't admit that the stuff they were teaching us was only interpretations of the writings of long-dead authors, and that there was no way to logically prove that the interpretations were what the writers really meant.
Read it again a few years later and realised just how good it was, but reading it first in English class just sucked all the enjoyment out of it, not to mention they randomised who had to read out loud in class and some of the (14 fucking year old) students couldn't read as well as I could when I was 3.