E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Tu fais suisse. You live alone; you are a misanthrope. Suisse means porter or door-keeper, hence Parler au Suisse (Ask the porter, or Enquire at the porters lodge). The door-keeper lives in a lodge near the main entrance, and the solitariness of his position, cut off from the house and servants, gave rise to the phrase. At one time these porters were for the most part Swiss.