American here, lived in Paris for a while.
Hmmm, I pretty good at it, but I don’t know if it’s actually looking at the person, or just from context. Like if I see a larger man wearing shorts in France (outside Paris and other places where Americans go) German is a safe bet, but if I saw the guy in a police lineup, I probably wouldn’t be able to tell him from most Americans.
Tanned skin with a mullet or mullet derivative spotted in Europe? Spanish. Male or female.
Russians have a look about them too. Something about the haircuts for guys and the overly made up look of the girls (with lots of accessories) and they often look serious.
French guys still wear rugby style shirts, and they hold their cigarettes differently than Americans. And they stick their lips out.
I can usually tell Japanese people from other Asians, and African Africans from African Americans; and usually down to West, Southern, or Eastern Africans. So I can tell a Kenyan from a Nigerian, but not a Nigerian from a Cameroonian.
Something about whitish Argentines makes them stand out too, my other Latin American friends say it’s because Argentines act like they are better then everyone else.
Lots of Americans would approach me in Paris and ask directions, they didn’t seem to know I was American at first, but they seemed to pick me out of a number of people to ask something, which I didn’t mind a bit. I think Americans may just look friendlier than the average Parisian, and I’m told by the French that our young men often have “military” hair cuts and that our women are really loud.
After I’d lived in France a while, someone on the train told me “You drop pen,” which I had. I thought, damn, how did he know? I thought I’d gone native. I’d let my hair grow out, and everything I was wearing from watch to sunglasses to shoes was Euro. Only after his friend got on the train did I realize he was American too, and spoke to me in “simplified English” because he thought I spoke French and he didn’t.
Brazilian men are usually kicking around a soccer ball and the women are usually naked. (Just kidding, but wouldn’t it be nice?)