It was a small program (2009?) that you could install, which allowed you to add a "Dislike" to any post on Facebook. However, it would only been seen by those who had the program installed themselves.
Anyway, the program spread like wildfire in a small group of people (including myself), but within five days, I stopped using it, since it doesn't add anything.
I agree: valuable things can't be conveyed by pressing a button.