Paralyzed from the neck up

Some people break their neck and are paralyzed from the neck down. That's horrible.

But some people are what I would call "Paralyzed from the neck up", i.e., they are walking around and doing stuff but their brain is stuck in dumbhead mode. Wake up, you! So when you are looking for a creative but not immediately obviously insulting way to describe, say, a dense cashier who doesn't understand why you're telling them they shorted you $10 change, and you go back to the car and your friend is like "What took so long?", you can say "Man, that cashier was paralyzed from the neck up. It was tragic." You're welcome!