Perhaps I am old-fashioned, but "proved" is a strong word for a two-day experiment of a single waitress with no control of outside variables.
It's a known fact better looking people get treated better by their fellow clothed apes in all walks of life, including and especially, service industry work.
A theory that "tips are always determined only by service quality" is indeed disproved by Myth Busters. But that's not what he said.