Before I begin, I feel it necessary to state for the record that I have personally screwed up each of these etiquette faux-pas. Often spectacularly, publicly, and with large numbers of Koreans staring at me... Well, except for the ones involving noses. I haven't had a cold, and I haven't met any small children that I was inclined to play games with. Anyway... Nonverbal gestures often speak louder than words in South Korean etiquette. So a few pointers to avoid embarrassing yourself and offending the people you meet:
Bow. To an equal, give a nice twenty to thirty-degree incline. To a boss or an elder, give a nice forty-five degrees or more. Whatever you do, don’t just nod. No, it is not a mini-bow. By nodding, you are saying you think you’re infinitely more awesome than the person you are greeting, and you can barely bring yourself to be bothered to say hello.
If a Korean offers a handshake instead of a bow, don’t just stick out your hand in return. Your off hand should be placed flat against the side of your stomach beneath your shaking hand, as if you’re wrapping the unused arm around your body. Alternatively, you can take your off hand and grip the wrist of your shaking hand, right about at the cuff of your shirtsleeve. Giving and receiving things follows the same rules. Buying a soda? Don’t just hand the shopkeeper your money with one hand. Just using one hand will give people the impression that you are being intentionally casual and impolite.
Never point with your pointer finger. It’s rude. In contrast, don’t be surprised if you see Korean people pointing with their middle finger. No, they aren’t trying to subtly flip you off.
Never make the “come here” gesture with your palm facing upward. Always do it with your palm facing downward. Palm up means that you’re summoning a dog. Palm down is normal and polite.
Never blow your nose in public. It’s fine to wipe your nose quietly in public. However, if you make a great honking sound into a handkerchief, say, on the bus or at the shop, you will immediately have every Korean in earshot staring at you in horror. They will then recount the tale of your bizarre rudeness to children and grandchildren for years to come (I’m not actually kidding or exaggerating here).
And speaking of noses. Please, whatever you do, no matter how cute the child you see, never play “got your nose.” If you aren’t sure what I mean, I’m referring to the gesture of placing your thumb between your pointer and middle fingers. Never, ever do this where anyone else can see you in Korea. I have no idea what the gesture means, and I don’t really know how to ask (since doing so would probably entail demonstrating the gesture). If you ever see someone giving someone else this gesture in public in Korea, run as fast as your foolish legs will carry you away from there because some crazy Quentin Tarantino violence is about to break out.
And lastly, smile. Smile when you say hello. Smile when you try your broken Korean. Smile in apology when you mess up and accidentally break one of these rules (except got your nose… you mess that one up, you’re on your own). You are a great big freaky westerner, after all. They may not like you, but at least they’ll forgive you.