1. Get a can of soda.
2. Poke hole in bottom of can with a skinny nail.
3. Drain soda from can.
4. Fill can with something! It doesn't have to be something gross, but the unexpected will cause a reaction! I've used sparkling water with no flavor with great results. Tap water will also work to simulate flattness. Tomato juice works good, too.
5. Cover hole on bottom with tape. (If you use something carbonated, seal edges of the tape with super glue.)
6. Put in fridge and make sure victim gets it. Or just hand it to him.
7. Watch and laugh!
I've gotten many different reactions from this. Some people freak out, even with water (it's not the taste so much as you do NOT expect water in your mouth when you open a can of Coke. Your brain just says STOP! THIS IS WRONG!!) They'll spit it everywhere! Tomato juice can be evil for this because it stains, and a lot of people will spit it out on themselves a little bit. You could try just switching sodas around (Coke in a Sprite can, and vice versa) if you don't want to be TOO evil.
