A pathetic way in principals thinking their punishing you, but really your just sitting at a desk for two hours reading, sleeping, going on the computer, or otherwise wasting part of your life while further putting off going back to your crappy home life, and that grounding you got for whatever reason your in friday detention in the first place. Oh boy, what a horrible thing.
Principal: I heard you cheated on a test.
Principal: You have friday detention. (haha, i hope they start to cry, for my horrible punishment that will shurley ruin their lives and make them never do bad again)
student walks away
Student: hurray, i get to put off going home for two hours. dumbass.