미친 (michin): This is the most common word for "crazy" in Korean. It can be used to describe someone who is mentally ill, or simply someone who is acting strangely or irrationally.
돌았다 (doratta): This word means "to be crazy" or "to have gone crazy". It is often used to describe someone who has suddenly or unexpectedly become crazy.
정신이 나갔다 (jeongsin-i nagatta): This phrase literally means "the mind went out". It is used to describe someone who is acting completely crazy or insane.
싸이코 (saiko): This word is borrowed from English and is used to describe someone who is mentally ill. It is often used in a negative way.
변태 (byeontae): This word is used to describe someone who is perverted or sexually deviant. It is often used in a negative way.