Obviously, mouth breathing is a health disorder where people due to
respiratory conditions, breath through their mouths.  Calling someone
a mouth breather is usually an insult referring to someone of low
class and intelligence.  What I'm looking for is the origin of that
insult.

Thanks in advance!

Hello jimv_atl,

A site by an American lexicographer for Oxford University Press traces
the pejorative meaning of "mouth-breather" back to 1944:

"mouth-breather"
Double-Tongued Word Wrester
http://www.doubletongued.org/index.php/dictionary/mouth_breather/

Incidentally, the online version of the Oxford English Dictionary
(available through certain libraries) does not have a citation for the
slang meaning prior to the 1985 Maclean's article.  It traces the
medical meaning back to 1910.

- justaskscott


Search strategy --

Searched on Google for:

"mouth breather" slang

Searched on online OED for:

mouth breather

Thanks!