Hold your phone in the right light and you'll see all the grimy fingerprint smudges on your beautiful black screen (this is also a great way for someone to steal your passcode). Same goes for your computer — put it to sleep and you'll be able to soak in the streaks of fingerprint trails.
There is now a way to prevent unnecessary touching.
A user on Reddit posted a program that makes your computer shout "Don't touch my screen, bro" whenever someone touches your screen. This is a not-so-gentle reminder to your friends who have a habit of leaving fingerprints behind.
See it in action: