I cheated a lot during high school.
I don't know why, really -- I liked school and was otherwise mostly a "good" kid. But some classes, I just couldn't be bothered to care. Very specifically, 9th grade biology.
Mr. Dieber was just kind of a jerk to us all the time, and a pretty hopeless teacher besides.
Anyway, somehow my friend Matt figured out where Dieber kept his answer keys in his office desk. The desk was locked, but Matt was good with locks. Dieber also had this tick of giving us pop tests and leaving the room. The next time Dieber sprung a "pop quiz" on us (it happened all the time), we knew just what to do.
I watched the door as Matt worked the lock. We copied the answers out onto a piece of notebook paper, returned the original answer key, and went back to class.
Then we made the mistake of passing around the answers.
When everyone got a perfect 100% on the test, Dieber knew something was up, but he couldn't prove anything. He never left the room during tests again, though.