UNPREPARED FOR TEST
You walk into class and realize you have a test you didn't study for. Go ahead and complete the test to the best of your ability, but just as a group of students walks up to turn in their tests to the professor, put yours in your bag and walk out. That same day go to your professor's office and ask him a question about something on the test. When he passes back the test, you can claim that you did not receive yours. Then remind him of your visit to his office during which you cited specifics of the test. The professor will assume that he lost it, and you will either get the class average as your grade, or get to take a make-up test that you can study for. Either way it's a lot better than turning in a guaranteed F.