Maths and PE! I couldn't (and still can't) grasp maths, I get numbers mixed up a lot and often need to use a calculator, even for simple calculations which most people could do easily in their head.
PE was also incredibly stressful for me. I hated the screaming and shouting of the other kids, I couldn't keep track of what was going on, and I was hopeless at all sports in general. Nobody ever wanted me on their team, not even my friends!