The cake is a LIE!

What is the origin of this internet fad? It's from the game Portal:

"You're a test subject that's working with new portal technology that works through a special gun. In order to test it, the company, Apeture Science, sends you through some rigorous test puzzles (about 18 or so, IIRC). Throughout the game, the main computer GLaDoS, tells you that after you complete all the test, you will be treated with cake.
As the screenshot showed, many of the insane who escaped pointed out that there is no cake, AKA the cake is a lie."
- Gamespot Forum

Now that you are armed with this new knowledge, go make silly pictures, like this: