머리가 나쁘다

You can use it to describe yourself or others. To say it politely, use 머리가 나빠요. For friends, use 머리가 나빠. If you are talking about a past mistake, use 머리가 나빴어. It functions like a standard adjective in Korean sentences. You will often see it in self-deprecating jokes. It is a very common, high-frequency expression in daily life.

Use it when you forget your own password for the fifth time. It works well when you fail a simple math problem. Use it with close friends when they do something silly. It is perfect for lighthearted venting about your own academic struggles. You might hear it in dramas when a character is frustrated. It is great for describing a 'clueless' character in a story.

Never use this with your boss or teachers. It is quite insulting if used toward a superior. Avoid using it with strangers or people you just met. Even with friends, be careful not to sound too mean. It can hurt feelings if the tone is too serious. Do not use it in professional performance reviews. It is too blunt for a formal workplace setting.

Korean culture places a massive emphasis on education and 'brain power'. Being called 'bad-headed' was historically a very harsh criticism. However, modern youth use it much more casually now. It is often used to excuse one's own mistakes. There is a cultural trope of the 'lovable fool' who is 머리가 나쁘다. It reflects the high societal pressure to be academically sharp.

머리가 안 좋다 is a slightly softer way to say it. 머리가 둔하다 means someone is 'dim-witted' or slow to react. 바보 is the noun for 'idiot' which often goes hand-in-hand. 대가리가 나쁘다 is a very slangy, aggressive version using a rude word for head. You might hear 머리가 잘 안 돌아가다 which means 'my brain isn't spinning/working'. Use these variations depending on how much 'edge' you want.