It might seem like a lot of detail to remember, but it's actually quite simple: know your Korean culture and manners. You meet your Korean sweetheart's parents for the first time only once, so why not cease the opportunity and make an epic, lasting impression? :)
Have at least the basic Korean phrases prepared. If you're not Korean, the parents will be more forgiving of your butchered pronunciation. If you're Korean by blood, regardless of where you were raised, you'll need to be extra alert. The parents will expect you to have decent Korean manners. Your actions will be seen as a reflection of how your own Korean parents raised you. To them, meeting you is an indirect way of meeting your parents.
What if you don't know enough Korean to carry on a conversation? Your actions will speak for you. Be polite and calm, smile when appropriate and be funny if you can do so gracefully. It's better to be a little quiet than overly loud. And ladies, as the Korean mother is preparing the home-cooked meal, ask her if she needs help in the kitchen. It's an opportunity to bond and show her that you know a thing or two about Korean food!
Your clothes will also speak for you. Wear something clean, conservative and semi-casual. Avoid short skirts, baggy pants, low-cut shirts and anything that makes you appear sloppy and/or seductive. Be classy. Clean socks are a must! Do you want to gross out the parents by wearing socks from last night's sweaty basketball game? You can never go wrong with white socks... until you accidentally spill something vibrant like kimchi on them. Grey is a safe color. Black is also good, but I personally find them mysterious. Black socks might secretly be dirty and can demand too much attention on light-colored floors. Make sure your toes are neatly trimmed. What if you need to take off your socks during the visit? You never know. Be ready for all situations.
If you haven't watched KWOW episode 81, what are you waiting for? (See above.)
Be the best of yourself and hope for the best. You can't force people to like you, but with a genuine smile and peaceful attitude, you can score some mega kimchi points. Good luck and have fun! Hope you can thank me in a couple years by sending photos of you and your Korean sweetheart's first baby :)
Helpful episodes: