GCSE Music.
I had only had practical lessons; no theory.
The teachers taught us nothing - focussing on coursework, until the last day of term where they gave us a revision guide to learn.
I had no real musical ear either, so questions like "Listen to the song and finish off the last 10 notes of the melody" were just impossible for me. The lack of theory compounded this.
I got full marks in coursework composition and nearly full in playing, then needed half marks or so in the exam to get an A* and I didn't
The exam was impossible!
I imagine my MEng 4year Mechanical Engineering Degree may be a shade harder overall though