I have visited Denmark and Sweden, and the most obvious change when you cross the border is that Danes rarely smile walking down the street (or talking to you), whereas Swedes look generally happy.

It is likely a cultural thing, as young (4-6 year old) Danes on the street do some happy, unlike their older siblings and parents;

I am aware that this contradicts surveys that conclude Danes are the happiest people and Swedes aren’t - just recounting my personal impression

These kind of things matter and are very rarely captured in statistics

My theory (as a Dane) is that Danish people get votes the happiest people because they are complacent.

But why do you need to look happy when you are happy? Asking as an Eastern European.

As an Eastern European living in America. These days I smile so much for no reason during the simplest interactions with people that I feel like an idiot. I'm not happy at all.

Where do you live? Having lived quite a few years in NYC I would say New Yorkers don’t smile much; at least not as much southern Californians.