Getting the most interactive presentation in an art class project, full of compliments by both the students and the teacher, only to find out I got a B- on the assignment. Especially when other students whose art looks kinda' cruddy got an A, all because I didn't strictly adhere to a certain set of standards (which I did, and I realize now why the professor had a surprised look when I explained my drawing process during the presentation) that actually allows you to draw like crap and still get an A.
I'm half tempted to spend a quarter of the time on my drawings and just stick to the guidelines now, screw actually trying to better my artistic skills and making the art look good, since apparently that doesn't count for anything.