I remember the first time I was in Chicago. I was walking around (smiling, of course) and I kept getting these looks from people--"She's weird! Is she dangerous?"--and after a while I realized I was the only one smiling. Everybody else was walking around as expressionless as they could get. It was the same when I went back ten years later. It must be a Chicago thing, not a Northern thing, because I didn't get the same reaction in Boston or New York or Philadelphia, even though (after Chicago I was observing) not very many people on the street smiled.
Humans are strange.