Certain aspects of Korean behavior might seem strange, odd or even offensive to people from Western backgrounds. So it's a good idea to be aware of them.
Crazy Drivers - Taxi drivers will be speaking on their cell phones and watching a soap opera on their GPS's while chasing through busy intersections and screeching to a halt when a car appears in front. All in a days work for them, but certainly upsetting to the fragile foreigner who's used to getting from A to B without fearing for safety.
Bus drivers are often jokingly referred to by foreigners as "Nasbus drivers", since they too, seem to chase down busy roads only to slam on the brakes before the next traffic light. So if you're using public transportation on the road: Hold on tight.
Public Affection - Public affection for romantic purposes is rarely seen and is in fact seen as rude and frowned upon. But affection between friends is very common and might be unnerving to Western people who frown upon people of the same gender holding hands or walking arm-in-arm. This is especially true with young girls or women, who will often dance together, or walk hand in hand when going to the movies.
Waiting a turn - The whole notion of waiting in line and forming an orderly cue is not as common as one might suspect. In a small densely populated country such as this one, queues are a foreign concept, and every person is used to pushing to get to the front. As a foreigner you will have to learn to grab your place, since, by patiently waiting for the next person in line to move away you'll find that you'll almost never get to the front.
Koreans push, shove and generally dart towards the counter, ticket machine, or whatever you're waiting for, so don't be surprised when someone simply walks (or pushes) in front of you. "Hey, I was here first!" will simply provoke quizzical looks. Once in Thailand, I was in line with a group of Koreans and when they pulled this very trick of jumping cue the immigration official stepped out of his little cubicle and had them line up. They're really not trying to be rude. Waiting patiently in line is simply not a concept they're used to.
Subway sardines - I lived in London for a couple of years, where the subway transportation system can get just a crowded as it does in Korea. However, I've noted that many other foreigners find the overcrowded trains seriously uncomfortable.
During peak hours, trains are very full, especially in the big cities. And just when you think there couldn't possibly fit another soul on subway car, another ten people will squeeze in. During peak times, steer clear of the doors as masses of people will often bump into you.
Motorcycle Mania - Motorcycles do whatever they want, whenever they want. There seems to be no rules for them whatsoever. They jump red lights and drive on sidewalks. They only thing they do do constantly is blow their horns, which, when you hear, you should hurriedly scramble away from.
Spitting - This one is probably the most irritating one to foreigners who come from Western cultural backgrounds. Spitting in public is very common and is usually deliberate and loud. Old men, young woman, kids and even grandma's participate in this practice which most of us will probably never get used to.
Getting your car parked in - It's a small country and most people have cars. So parking is very limited and cars are often parked in. To overcome the barrier of having your car parked in, all Korean cars feature the cell phone number of its owner on the car's dashboard. This way you can phone whoever's blocking you in and have them move their car so you can be on your way.
Public Urination - Koreans don't seem at all shy at this bodily function. Mothers will often hold their kids over sewer grates to relieve themselves and older men will often urinate in public, even though a toilet is probably somewhere close by. Bathrooms are often built so that the main door opens up on the urinals (in the men's case). In general, Koreans seem to be less private about this, than most Westerners.