in (one's) right mind

Thinking soundly; rational. Usually used to set up a context in which any sane person would or could do, say, or think a certain thing. No one in their right mind agrees to those kind of terms—unless they sign a contract without reading it. You must not be in your right mind if you think that breaking up their wedding is a good idea. Do you have a death wish? No one in their right mind would hitchhike in this day and age!

(not) in your right ˈmind

(not) mentally normal: Nobody in their right mind would buy a used car without driving it first.