out of one's mindLiterally means “not in one's right mind.” It can describe someone acting irrationally, wildly, or as if they are not mentally sound; the tone may be serious or exaggerated depending on context.
KO: 그렇게 위험한 일을 하다니 제정신이 아닌 것 같아.
EN: You must be out of your mind to do something so dangerous.