I came up with this prank while at school, Fellow classmates would always forget their pencils or pens and always asked to borrow mine. Well I got tired of that and decided to teach them a lesson.
One day I booby trapped a pencil using soy sauce.
It's a very funny prank and will get your point across, Check out the video tutorial for full instructions on how to do this along with a demo.
Start your career in Graphic Design with the WonderHowTo's Beginners’s Guide to Photoshop Course