Nerds who know just about everything and practice anal alpinism with the teachers. Bullies who make your class time really tough. Or just people you simply don't like because of they appearance or behavior. Your education can be quite difficult and only you know people responsible for it.
The question is – can you do something radical to turn things around? Yes. You can send them the piece of shit they deserve. But before you do, think about what message you're trying to convey.
Do you want to let your classmate know that he or she is disgusting and dirty? Go for the pig shit, its stench is remarkable compared to its size. Do dumb people annoy you? Order them a shit from a donkey – a classic mound of roughly 2 inches long shits. And if you seek just a general form of revenge, either horse or cow shit will do the trick.
After you choose the best piece of shit for you needs and make an anonymous order, you can have the package delivered straight to your classmate – or get it yourself and prepare a more hideous way of handing it over.
How about a great public performance? Everything you need to do is to sneak to your victim’s locker and hide the shit there. Or you can wrap it up a little gift and hide it in his school bag. Just imagine how the recipient finds a present, unpacks it in public and everybody would see the shocked expression full of revulsion... Don’t forget to take a camera!