I'm a Doppelganger?

I've yet to understand this phenomenon. I seem to look like other people. Or, there seems to be people out there who look just like me. At least, that's what many of my patients or family members say to me.

They say, "What is your last name?"

I tell them. And they say, "Oh, then you're not who I thought you were."

"Who did you think I was?"

"Well, you look exactly like Bob Whatshisname. You are a spitting image of him."

"Oh," I say, "You mean I'm a doppelganger?"

"A what?" they always seem to ask.

"A doppelganger. It means that you look just like someone, although you're not related."

"Oh!" they say "That's a neat term. You have a good vocabulary."

So, apparently I'm a doppelganger. How's that for a fancy term?