checkup from the neck up
if you think you can get away with driving 50 more miles with the 'empty' light on, you need a checkup from the neck up
suggesting this is a way of saying someone is talking or acting crazy
"if you think you can get away with driving 50 more miles with the 'empty' light on, you need a checkup from the neck up" What is the definition of "checkup from the neck up"?