That's easy, foreign languages. I have never been good at them, the only exception is English (but you hear it constantly on the television, read on the internet, etc.) . I could never remember the words. And there were 3 foreign languages mandatory for 4/6 years (English, German and French) . But so many languages, I doubt there are many countries where there are so much mandatory (I live in the Netherlands). Literature wasn't very pleasant either, I just dislike being forced to read books.
History can be quite nice, if you have a teacher that knows what he is talking about, links the different facts to make it clear for you why certain decisions were made. Lessons about religion can be quite fun, also here it is very important to have the right teacher. They must be able to make a story of it, otherwise it is very boring for me. I find it interesting to learn about the different visions on the world, though I realised that only recently. Any Science subject, and/including maths was too easy for me, I'm just too good at it.
Also, I found it very boring to write essays and therefore I disliked quite a few courses, though I liked the subjects that were taught. I never had any trouble with too religious teachers, none of my teachers taught there subjects in a religious way. The only thing close was the biology teacher how is a Darwinian and finds the creationist thinking ridiculous. He made some jokes about a a big book send by creationists to promote there ideas on schools.