This is one of the funniest pranks I've seen. No one gets hurt, just embarrassed and it's very clever.

So, the prankster asks a stranger in the library to watch his laptop, so he can go use the bathroom, or do some sort of task.

The stranger agrees, but doesn't know the prankster can control the computer with his phone.

The keyboard on the laptop has been disabled, so it doesn't do anything. Which means you can't shut off videos and turn down the volume.

A minute or 2 after the prankster leaves, a pornographic film pops up on the screen and the audio is on full blast!

Obviously, the stranger babysitting the computer is mortified and embarrassed beyond all belief as the other folks in the library start laughing and staring.

Brilliant!