Generally occurs at the end of the school semester and the beginning of
exam week. You ask your professor/teacher what to study for the
Final Exam. They
tell you what isn't going to be on the Final Exam or, they tell you what isn't going to emphasized in great detail. Contrary to what they told you, they end up putting that AND ONLY THAT on the final, thereby causing you to fail for the semester resulting in you having to repeat the course next semester.
Kid: She told me it wasn't
on the test. I didn't study it... She
put it on the test. I failed it.
Other Kid: Ah, the old
summer school sabatoge.