be soft in the head
To be dumb, foolish, or witless. You sold the car and bought a scooter? Are you soft in the head? Tommy's a good kid, but he's a little 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.