Mine was Geometry/math in general-- not because I sucked at it, but because I got the short straw too many times of having shitty, pre-occupied teachers who thought copying examples straight out of the book made for teaching.
I'd say PE, but PE in high school was better 'cause it was something other than HERE RUN LAPS. I couldn't do laps well, but when it came to sprinting, I was among the top. D: