This is a counter prank I did as a teacher on a student who tried to prank me.
A different student had a hard time staying in his seat the whole class. I asked what it will take him to stay in his seat for 45 minutes straight. He made me a deal that I have to memorize the first hundred digits of pi (and write it on the board in front of the whole class) if he stays put for one whole class.
Sure enough, a few weeks later he some how stayed put for an entire class. After class he announced that during the next class I will be writing the first hundred digits of pi on the board from memorization.
Of course I knew what at least one wise guy was going to do and I had to come up with a plan for a counter attack.
Before class I found two different text books that had the first few hundred digits of pi and copied those pages for the class. At the end of class I wrote the 100 digits on the board and I heard some whispering that most of the numbers were wrong. Then I gave out the photocopies so that everyone can see that the numbers were correct.
“But Mr. Pepper”, one student chimed, “the last 80 numbers are different from the numbers on the paper that Heshy gave out”!
“Well”, I said, “Let’s ask Heshy how he calculated the numbers, he must have used an approximation method that is only valid for the first 20 decimal spots or so”.
Heshy admitted that he tried to prank me by giving everyone the fake numbers so it will look like I made it up.
As I was erasing the board and dismissing the class I announced with a straight face that “as always, anything I write on the board, whether it is in the book or not, is fair material for a test”.