I'm not being rude, I just don't know you

Looking in the eyes, smiling, and hellos will get you nowhere. If anything this will cause some confusion on the receiving end. "Do I know you?"

There's no such thing as letting someone go ahead to get on the elevator, bus, holding a door, move through the aisle at the grocery store, etc. Koreans generally place a non-receptive distance between themselves and strangers in public (watch out for umbrellas). Basically I expect to constantly bump into people without apology. There is a public sense of privacy. You just don't make eye contact with people in the sort of way where you acknowledge them, even on a crowded bus where you're standing hip to hip and leaning over someone's seat, (this does cut out some awkwardness).

Then there are the ajummas the notorious Korean older women who in my experience and through stories I have heard "dish it out". They've been through it all and they don't apply conventional and unnecessary politeness. Comical. I had one basically sit on me on the bus today. Or... I'm in the supermarket checkout line when an ajumma who is standing behind me in line gestures to her friend who is waiting outside of line, they go ahead of me to the front of the conveyer where my groceries are piling up and she and her friend just stare at me and my things. So I give them a little nod, like "hi" to invite any conversation or charades (still lacking Korean language skills at this point) and they just stare through me and talk (presumably) about me. When I have to maneuver around them to the debit card machine they stay anchored. Blocking. So I have no choice but to give them a little shoulder bump.

A tip for travelers:

Home Plus is a supermarket with (supposedly) the lowest prices and just about everything: stationary, clothing, shoes, cosmetics, groceries, common car parts, electronics, etc.

They carry Tesco items (Tesco is an EU supermarket) so you can find coffee beans, canned baked beans, spaghetti sauce, wine, carrot juice, dijon mustard. -Sometimes you want chili beans and cheese.

Home Plus is really entertaining. Not only are there hundreds of people to bump into and ignore but in store advertising is live and pretty aggressive. Lots of shouting sales people and sales women with little visors over their mouths grabbing people to feed them samples. The place is like a buffet of samples including wine.

There's a tasty food court with beautifully shellac-ed display foods to choose from,which is helpful if you don't know the name of a dish. Another option is inside the actually grocery store in addition to all the samples there is a "soup island" where you can eat fresh noodle soups.