The one about the fun GP lesson.

It's not everyday that GP is fun, and it's definitely not everyday that you get to play an online game during the lesson.
mcvideogame.com
It's a simulation about managing the McDonald's Corporation where cows are burnt to ciders by a gargantuan torch if they've disease, employees spit in the people's food, and you get to corrupt important people to avoid lawsuits -what fun!
Five minutes into the game, the room was filled with a chorus of
"Zomg, where aren't there any cows??"
"Hahaha, my employee just spit into the customer's food and smiled!"
"HUH, my cow just turned green"
"Let's go corrupt another official!"
"My cow just turned into a skeleton, wth???!"

Now tell me how GP can't be fun.