This facebook easter egg trick is based on the Konami Code which is one of the most famous cheat code in video games. The Konami Code has been used in countless games and is now used on facebook to activate the secret easter egg which is the facebook lens flare.
To try out the secret hidden facebook code for yourself, make sure you are on a facebook page.
Then press: UP UP DOWN DOWN LEFT RIGHT LEFT RIGHT B A ENTER on the keyboard.
You should then see the cool facebook easter egg lens flare on your screen. To remove the lens flare just REFRESH the page.
You could post the hidden facebook code in your status or you could do it on your friends computer!