Certain small things are common here that, from the perspective of American culture might seem quite odd. Meaning in terms of behavior and practices.
One thing I've seen, more than once, is the well-dressed businessman – slacks, suit jacket, maybe even tie – standing on a corner, hailing a cab or talking on his cellphone… but wearing flip flops on his feet. I think this is related to the fact that most Koreans take their shoes off upon entering people's homes, and even in some businesses, such as very traditional restaurants. So people give up the pretense of wearing nice shoes, and just stroll about with socks and flip flop sandals on.
Another thing that I've seen, more than once, is a child walking alone down the street – say, 7 or 8 years old – well after dark, with an umbrella swinging from one hand and a talking on a cell phone laconically, looking for all the world like a world-weary adult heading home from a stressful job. It's a bit disorienting, given how protective we are in the US of children – but of course the streets are likely much safer here. And, on the other hand, although children seem in some ways less world-wise here, they are often well-trusted and expected to behave in remarkably adult-like ways, in others.