This was used in the US TV series Stranger Things (S01E03, 2016):
I was tripped by this mouth breather, Troy, okay?
Yeah, you know a dumb person.
(Stranger Things S01 was set in 1983, but may or may not be historically accurate with regard to this piece of slang.)
I have two questions:
- Roughly when and where did this slang start being used? (I assume this slang originated from the perceived inferiority of mouth breathing as compared to nose breathing.)
- Are there specific regions of the US or world where this slang is commonly used? (It is my impression that only some Americans use this slang at all. And even in the US it does not seem to be widespread.)
From Popular Science Monthly (Dec 1892):
From the condition of a "mouth-breather" it is but a short step to one of two results—more often both: deafness, and that peculiarly stupid, sleepy, inane, foolish expression of countenance so characteristic of the "mouth-breather".
From Adenoid Vegetations of the Naso-pharynx (1892, p. 3):
The action of these distorted muscles upon the soft and pliable bone of the child's face, together with the absence of admission of air to the accessory nasal cavities,—the frontal, sphenoidal, ethmoidal, and maxillaries,—causes a deficient development of these sinuses, giving a flat appearance to the cheek-bones, producing a peculiar physiognomy characterized by the open mouth, vacant stare, and almost idiotic expression of countenance. The hanging lower jaw and constant mouth-breathing, together with deficient development of the bones constituting the nasal septum and with augmented atmospheric pressure upon the roof of the mouth, cause a high-arched hard palate. ...
Dr. Casselberry, of Chicago, says, "Not only do these unfortunates look stupid, but they really are stupid, and exhibit abundant evidence of mental hebetude, with inability to fix the attention to learn, to memorize, or to reason, the whole evidencing an impairment of cerebral function which Dr. Guve. of Amsterdam has recently described under the name of 'aprosexia nasales' ...
Another 1889 publication:
Mouth-breathing of many years changes the aspect of the face. The open mouth, the protruding teeth of the upper maxilla, the disappearance of the naso-labial folds give the face a stupid expression.
Of course, these quotes taken from more scientific/medical contexts do not directly address my questions above on when/where this slang began to be used or remains in common use.