I took 3 AP test during my time in high school. I miraculously pulled out a 3 on the AP Physics test, without having much of a clue what I was doing, when I was a junior. Then senior year I somehow managed to get a 1 on AP Chemistry (the kid who slept through most of the test next to me got a better score than I did) and a 5 on BC Calculus.
I blame the dreadful chemistry score on the fact that I just did math in the back of the room the entire time we reviewed, which still makes it my fault but I feel better about it that way.