A mental health examination.
Suggesting this is a way of saying someone is talking or acting crazy. Used to express disbelief, skepticism, or simple mocking. Indicates a level of ridicule serious enough to move the subject away from what the other person has said, and onto the state of mind of the speaker.
"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."
When a girl has a nice body, but her face is busted!
Playa 1-"Yo, shorty's body is tight!"
Playa 2-"Yeah, but peep her face. She needs a checkup from the neck up!"