Green’s Dictionary of Slang

(US) boastful, self-aggrandizing.

1886		Nat. Police Gaz. (NY) 28 Aug. 14/2: The big blow heart [sic] Chicagos feel greatly chagrined over the three straights they dropped in New York city.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 217: blow-hard, boastful.
1939		in W.C. Fields By Himself (1974) 225: In his familiar blowhard manner, Mr. Whipsnade sets to work.
1957		(con. WWII) ‘Weldon Hill’ Onionhead (1958) 15: This blow-hard barber with his windy stories [...] his impossible lies and bragging.
1971		B. Malamud Tenants (1972) 122: And I see that you a mammyrammer blowhard fart that has no respect for hisself.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 40: I cannot help but think of your blowhard client, James Riddle Hoffa.
2004		Mad mag. Jan. 24: A shrill, blowhard, liberal columnist.
2021		J. Ellroy Widespread Panic 4: [B]lowhard bloggers and their tattle texts?