Guess what's the above picture?
If your guess is blue screen of death you are correct!
I have some nice collection of computer pranks for you, some are completely harmless (unless they don't know how to revert back) to some that can crash your computer and literally kill your computer (as in kill).
Here are some of the 3 pranks: (Please do not attempt this on your computer)
1. Creating 1000's of folders completely automated