A British man came to a Sheikh and asked: Why it is not permissible in Islam for a woman to shake hand with a man?
The Sheikh said: Well, Can you shake hand with Queen Elizabeth?
British man said: Of course not, there are only certain people who can shake hand with Queen Elizabeth.
Sheikh replied: Our women are Queens and Queens do not shake hands with strange men.
Prophet Muhammad (pbuh) said: "For one of you to be stabbed in the head with an iron needle is better for him than to touch a woman who is not permissible to him." At-Tabarani (sahih)