Etymology: a common practice among sophisticated women after being proven wrong is to scratch their necks, while looking off or away. This action is rarely done by arrogant people when proven wrong. Because of that, This phrase is used to let them know what they need to do, since they are wrong.
Perosn 2: For soft skin you should try Vit E.
Person 1: Vit B is the oil I need for good skin THANK YOU
Person 2: WRONG, Vit B is water-soluble therefor not an oil, Vit E is an oil.
Person 1: Really!
Person 2: Yea, Really. Scratch your neck!(or scratch your dirty neck)