go soft in the head

go soft in the head

To become dumb, foolish, or witless. You sold the car and bought a scooter? Have you gone soft in the head? Tommy's a good kid, but I think he's gone a little soft in the head.
See also: head, soft

be/go soft in the ˈhead

(informal, disapproving) be/become crazy or stupid: Sometimes I talk to myself in the street; people must think I’m soft in the head.
See also: head, soft