not be all there
be not all there
1. To not be mentally sound; to be crazy or mentally deranged. A: "Look at that guy talking to himself on the corner." B: "I reckon he's not all there."
2. To not be very bright or intelligent; to be dimwitted. Jim's a nice guy, but with some of the foolish things he does, I think he's not all there.
not be all thereINFORMAL
If someone is not all there, they are not very intelligent, or are slightly crazy. I tried to talk to her but she wasn't really all there.