This prank lets you freeze your victim’s phone (temporarily!). You'll need to choose a victim who has trusted you with the password to their phone (and who has a fine sense of humor).
Start by taking a screenshot of the phone's home screen.
Drag all the folders and apps to the right until they move to the next screen.
Find the screenshot you just took in the Photos app and set it as the home wallpaper.
Then put the phone back where you found it and act very concerned when your victim tries in vain to use it.