Green’s Dictionary of Slang

1. (orig. US) boastful, arrogant, vulgar.

1885		C.F. Lummis letter 10 Jan. in Byrkit Letters from the Southwest (1989) 240: Lockhard, who turned up again, more pig-headed and loud-mouthed and disagreeable than ever.
1903		Seattle Repub. (WA) 17 July 2/3: The giggling girl may sober down when she gets older, but the loudmouth girl is likely to become louder.
1905		Muskogee Cimiter (OR) 17 Aug. 4/2: If some one would muzzle the loud-mouth blatant Negro Demagogue the conservative members can accomplish something.
1914		M. Glass Potash and Perlmutter 144: Sure I know him – a loudmouth feller, Mawruss; got a whole lot to say for himself.
1918		Hall & Niles One Man’s War (1929) 306: One particularly loud-mouthed bozo [...] said, ‘You’re pretty foxy, ain’t you!’.
1922		‘Brag And Boast’ in T.W. Talley Negro Folk Rhymes 213: Dat big loud mouf Nigger.
1929		‘Ellery Queen’ Roman Hat Mystery 76: Best I could get for that loud-mouthed shrimp!
1935		C.G. Finney Circus of Dr Lao 14: Larry the infantryman, Larry the booze-fighter, Larry the whorechaser, Larry the loud-mouthed.
1945		(con. 1928) R. Westerby Mad in Pursuit 106: Steve Fenn and that bunch. Loud-mouthed fatheads.
1947		B. Schulberg Harder They Fall (1971) 80: All these books [...] had given her a point of view from which to criticise Nick and his loudmouth friends.
1953		L. Uris Battle Cry (1964) 291: We got to take that loud-mouth bastard?
1959		E. De Roo Go, Man, Go! 99–100: They didn’t go out with other members’ bams or anything as lousy as your rap. They was just cheesy and loud-mouthed.
1960		D. Hamilton Death of a Citizen 28: By morning I could be in Texas. Normally I have a good New Mexican’s aversion to that loudmouthed state and all its residents.
1969		C. Himes Blind Man with a Pistol (1971) 179: The loudmouthed soul brother was sitting in the first cross seat facing toward the rear.
1969		‘Iceberg Slim’ Pimp 214: A loud-mouth joker beside me was arguing with stud on his other side.
1973		G.V. Higgins Digger’s Game (1981) 11: Give the loudmouth bastard what he wants.
1982		P. Barker Union Street 199: He drinks, doesn’t he? Loud-mouthed git.
1989		Viz June/July 4: I’m sick of loudmouth celebrities.
1993		M.B. ‘Chopper’ Read How to Shoot Friends 98: To me revenge is a holy duty. It is not something to be loudmouthed about in pubs.
1994		N. McCall Makes Me Wanna Holler (1995) 172: The hustlers, the thumpers, the loudmouth bluffs.
2001		A. Sillitoe Birthday 189: His loudmouthed humour was laced with cunning.
2011		G. Hayward Corruption Officer [ebk] cap. 29: It was the loud mouth kid that invited to female C.O. to his private parts the other day.

2. (US) ostentatious, showy.

1979

‘Iceberg Slim’ Airtight Willie and Me 46: My old man copped some loud mouth suits.