잘 잤어?

You say this the very first time you see or text someone in the morning. Keep your voice light and slightly rising at the end. It’s a question, but you don’t need a detailed report on their REM cycles. A simple "Yeah, you?" is the standard reply. If you're texting, adding a sleepy emoji makes it even better. Just don't say it at 2 PM unless they just woke up from a massive nap.

Use this with anyone you use informal language (반말) with. This includes your close friends, siblings, or younger cousins. It’s perfect for a roommate stumbling into the kitchen. It’s the go-to text for a significant other to start the day. You can also use it with coworkers you are very close with outside of work. It creates a cozy, intimate atmosphere immediately.

Never use this with your boss or your grandparents. That would be a major social faux pas! For elders or superiors, you must use the formal version: 안녕히 주무셨어요?. Using the casual version with a teacher might get you some very confused looks. Also, avoid it if you're meeting someone for the first time. It’s a bit too 'cuddly' for strangers. Stick to a polite 안녕하세요 (Hello) in those cases.

In Korean culture, greetings often revolve around health and basic needs. Asking if someone slept well or ate well is a sign of affection. Historically, life was tough, so these questions were genuine checks on a person's condition. Today, it’s a remnant of that caring mindset. It shows that in Korea, your well-being is a communal interest. It’s a small way of saying, "I’m glad you’re okay today."

If you want to sound even cuter, you can say 잘 잤어용? (adding a 'y' sound at the end). For a slightly more masculine or blunt feel, some might just say 잘 잤냐?. If you are talking to a group of friends, you still use 잘 잤어?. If you want to ask if they had a 'honey sleep' (a very deep sleep), you can say 꿀잠 잤어?. 꿀 means honey, and it’s a very popular slang term.