When a guy has a girl get on her knees and sticks his erect penis against her neck, underneath her chin. He then grabs the back of her head forcing her to look downward holding his penis between her neck and chin, and proceedes to thrust back and forth.
Someone who is so fucking useless their body only functions from the neck downwards, completely independently of the brain, resulting in someone who literally isn't worth a wank
You say this when you get annoyed on the phone and are about to hang up. Since you’re leaning your head to be on the phone, the person on the other end is fuckin up your neck and wasting your time.