Coffee Snobs: Do you wash your coffee cup?

I work with a guy who is a confessed Coffee Snob. He used to work in a high end coffee shop.

The other day he said that he once washed all the coffee cups for everyone that worked there (personal cups, of course) and they got mad at him.

They told him that you never wash a coffee cup. You rinse it out, sure, but not actually wash it. Washing it means washing out some of the coffee flavor. I guess from the brown crud that accumulates on the inside.

So, do you wash your cups or just rinse them out? Frankly, I’ve never heard of this before.