I don't understand my students who think that they are going to show/teach me/their parents/the system/the MAN a lesson by purposely failing a class.
EDIT: I am not talking about students who do not understand. These students I'm talking about CAN do the work. When they do turn in homework, or take the test - they score high. These are not students who do not understand. But they purposely do not do homework, or turn in tests blank.