E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To astonish the Browns. To do or say something regardless of the annoyance it may cause or the shock it may give to Mrs. Grundy.
Anne Boleyn had a whole host of Browns, or country cousins, who were welcomed at Court in the reign of Elizabeth. The queen, however, was quick to see what was gauche, and did not scruple to reprove the Browns if she noticed anything in their conduct not comme il faut. Her bluntness of speech often astonished the Browns.