One day while we were walking the sun came out for just a minute - a fairly rare occurrence during a Ukrainian winter, and I walked around the streets beaming. When I started talking to a man, he stopped mid-sentence and said, "Are you high?"
I figured what he was saying was in regard to our talking about the Bible (he certainly wouldn't have been the first to ask that question with regard to religious belief), but he legitimately thought I was high. He went on to say (I paraphrase), "You're just walking around the streets talking with people, seemingly fascinated by anything I talk about, and with a big grin (усмешка) on your face. That's not normal."
And, to be fair, it was pretty rare that I was in such a mood.
If you think about it, the smile that Americans force a lot of the time is very fake. Think about families smiling in their pictures - they look vaguely happy, but there's a noticeable difference between that and when you can see a genuine smile. If you're a Russian, why pretend? And while I still smile in pictures, I can see their point.
When I got back to the US after having been in eastern Ukraine for two years, I got the opposite reaction. "Are you depressed?" or "Are you doing OK?" While living in Ukraine had been a culture shock and forced me to see the world quite differently than growing up in small-town Utah suburbia, I was by no means depressed. I just held myself in a different way. I also spoke more with exaggerated hand motions, had different intonation, and was shocked at how I could give a $100 bill to a cashier at the grocery store without getting in trouble.