> To presume someone is stupid if you see them laughing is certain a cultural thing. Here (US) we'd probably just assume they were happy. But on the flip side,

> To presume someone is stupid if you see them laughing is certain a cultural thing. Here (US) we'd probably just assume they were happy. But on the flip side, a lot of people in the U.S. would assume someone is sad or angry if they are not smiling. There are examples in comments here.