The writer and critic H. L. Mencken (1880-1956) coined the term “booboisie” (boob + bourgeosie) in the Baltimore (MD) Evening Sun on February 15, 1922. Mencken meant to describe a middle America often ignorant on the issues.
 
Mencken’s term “booboisie” has frequently been spelled “boobeoise.”
 
       
The Free Dictionary
boob·oi·sie (bbwä-z)
n.
A class of people regarded as stupid and gullible.
[boob + (bourge)oisie.]
 
Free Merriam-Webster Dictionary
bour·geoi·sie noun \ˌbu̇(r)zh-ˌwä-ˈzē\
Definition of BOURGEOISIE
1: middle class; also plural in construction : members of the middle class
2: a social order dominated by bourgeois
Origin of BOURGEOISIE
French, from bourgeois
First Known Use: 1707
 
Wikipedia: H. L. Mencken
Henry Louis “H. L.” Mencken (September 12, 1880 – January 29, 1956), was an American journalist, essayist, magazine editor, satirist, acerbic critic of American life and culture, and a student of American English. Mencken, known as the “Sage of Baltimore”, is regarded as one of the most influential American writers and prose stylists of the first half of the 20th century. Many of his books are still in print.
 
Mencken is known for writing The American Language, a multi-volume study of how the English language is spoken in the United States, and for his satirical reporting on the Scopes trial, which he named the “Monkey” trial. In addition to his literary accomplishments, Mencken was known for his controversial ideas. A critic of the Second World War and representative government, Mencken wrote numerous pieces about current events, literature, music, prominent politicians, pseudo-experts, temperance and uplifters. In particular, he critiqued anti-intellectualism, racism and bigotry, populism, creationism, Fundamentalist Christianity, organized religion, the existence of god (Mencken was a staunch atheist), osteopathy, and chiropractic.
 
Google Books
>Cassell’s Dictionary of Slang
By Jonathon Green
Cassell
2006
Pg. 156:
booboisie n. [1920s+](US) respectable fools, considered as a class in their own right; a synon for modern “middle America”. {BOOB n. + bourgeoisie. Coined by H.L. Mencken as part of a list of words describing "the victims of the Depression, then current" and published in the Baltimore Evening Sun on 15 February 1922 in a list of 50 similar terms, including boobariat, booberati, boobarian]

22 February 1922, Montgomery (AL)

, pg. 2:
PLOT TO MULCT "BOOBOISIE" REVEALED
BY ARRESTS MADE IN MOBILE TUESDAY
Belief Expressed That Men Held in Mobile Are Members of
Gang WHich Are Said to Have Attempted Get-Rich=
Quick Scheme on Ohio Farmer
(Associated Press)
NEW YORK, Fed. 21. -- A plot to mulct the "booboisie", which might have been invented by an author of the get-rich fiction was revealed by the Burns Detective Agency here today with the arrest at Mobile, Alabama, of seven alleged wire tappers, believed to be members of a gang which formerly operated in New York.

23 April 1922, Springfield (MA) Republican, pg. 27, col. 8:
[A. B. W. in London Times.]
Booboisie is what ji, Pinkerton would have called a boss word. Presumably it si formed by analogy from Bourgeoisie. I think I know what it means: it must be the equivalent of Ibsen's "compact majority" and Carlyle's "mostly fools."

Need I say that it comes from America? It has been invented by two critics in collaboration, H. L. Mencken and G. J. nathan, and, obviously it has been coined as a word of contempt. But I am in doubt whether these two gentlemen do not sometimes, as an act of grace and favor, themselves write for the booboisie. For they are now and then dreadfully behind the times, and not seldom -- what shall I say? == boobois.

14 August 1922, Arizona Republican, "Our Wealthy 'Booboisie,'" pg. 8:
But you are accepted by what Mencken might call the wealthy "booboisie" -- the circle Mr Harding frequented before he was advanced to the White House.

Google Books
September 1922, The Smart Set: A Magazine of Cleverness, “Repetition Generale” by H.L. Mencken and George Jean Nathan, pg. 44, col. 2:
in exactly the same way the American (Pg. 45—ed.) booboisie will cease to be democratic on the day following the day that the Man on Horseback gallops up the White House steps.
 
Time magazine
FICTION: Bible Boar
Monday, Mar. 14, 1927
(...)
The spokesman (Frank Shallard) has faith of a variety too subtle for what the Castigator’s friends call the “booboisie.”
   
Google News Archive
17 October 1927, St. Petersburg (FL) Evening Independent, “Mussolini and Mencken enemies of democracy, is priest’s charge,” pg. 13, col. 3:
He cited the following list of terms culled from Mencken’s book, “Note on Democracy”:
 
“Booboisie, the city moron, country yokels, righteous clodhoppers, hinds of Dayton (Tenn.), anthrapoidal proletariat,” and Mencken’s assertion that American people were “Sheep, goats, donkeys and jackasses.”
 
Time magazine
Books: Laureate of the Boobolsie
Monday, Oct. 08, 1945
CASS TIMBERLANE—Sinclair Lewis—Random House ($2.75).
   
Google Books
H.L. Mencken:
A portrait from memory
By Charles Angoff
New York, NY: T. Yoseloff
1956
Pg. 101:
He called them the “boobeoisie,” a term that Lewis almost never used.
 
21 May 1994, Waterloo Record (Kitchener, Ontario), “Shrewd insights from a skilled diplomat” by J. L. Granatstien, pg. D4:
Clearly, Reagan was merely the triumphant representation of the American boobeoisie in power.
 
Infowars.com
Corporate Poll Reveals Boobeoisie Fooled Again on Budget
Kurt Nimmo
Infowars.com
April 29, 2011
It’s a testament to the effectiveness of the corporate media. According to yet another poll, the little people think for some reason establishment Republicans will do a better job dealing with the “budget,” that is to say taxing and spending – or more accurately, borrowing from bankers and then shuffling off the debt payment to future generations.