Keep in mind that this is an easter egg, so you basically get nothing from it.
To start, you need to get a Sniper rifle from the box, this can take you various attempts to actually get. Once you have one, all you do is make your way to the roof where you build the plane. Once you are there, walk toward the back of the area, and scope outward toward the sky. As you are scoped in, a face will appear and you will hear a loud scream.
This can be very frightening to those certain people.