Human Anatomy
the material isn't hard but there's so much of it that I'd spend hours upon hours each week preparing for tests
Memorizing muscle names, locations, their insertion and origins, what type of motion they contributed to, and what type of lever systems they are -- in addition to spelling them all correctly -- in the span of a few weeks nearly sent me over the edge
My professor was known for asking tons of trick questions on exams. I'd be taking his tests and cursing at him in my head the entire time