In Reply to: Barber's knock posted by Tony Tolley on November 14, 2009 at 13:57:
: Please can anyone advise where the phrase "barber's knock" comes from? My dear mother used to say it to me when I had had a haircut. She would say you've had the barber's knock.
I am guessing that she was referring to "shave and a haircut..." See "knock on wood," http://www.phrases.org.uk/bulletin_board/60/messages/645.html