worst class I ever took was a seminar titled Native Americans in Modern Pennsylvania during my senior year of college.
I needed a humanities seminar in order to graduate and it was the only one being offered during the fall before my last semester. it wasn't difficult perse, just
soooooooooooo boring and the professor was a real d-bag.
in terms of sheer difficulty, my honors bio class during sophomore year of college really pushed me the most. it also helped me learn some completely different ways of learning, though, which really helped in later years of college. there was no text book or lab manual for the class and the prof
would not allow note taking or lecture recording. it was rough, but it forces you to pay attention, ask questions, and make sure you're really understanding what's being taught instead of just writing down as many notes as possible and hoping to cram it all back in the night before the final. after that class, I never had to take a ton of notes or do any cramming again. my profs always looked at me weird when I sat in classes and didn't take any notes whatsoever, but they'd usually stfu after the first exam
