Green’s Dictionary of Slang

very bold.

1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Bold. Bold as a miller’s shirt, which every day takes a rogue by the collar.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

arrogant, impudent, outspoken, shameless.

1781		G. Parker View of Society II 215: Those comments we hear after our Tyburn executions of ‘He died hard,’ and was ‘as bold as brass’.
1789		G. Parker Life’s Painter 162: He died damn’d hard and as bold as brass. An expression commonly used among the vulgar after returning from an execution.
1819		Cobbett’s Wkly Political Register 13 Nov. 12/2: Any other man [...] would have sneaked away into some cockloft and hanged himself [...] But he comes out as a bold as brass.
1824		Chester Chron. 29 July 3/5: He came to him ‘as bold as brass’, with a pipe in his mouth, beastly drunk.
1831		Nottingham Rev. 25 Nov. 4/1: So tight and small their breeches grew, / It roused the People’s passion; / The snips however, bold as brass, / Declared it was the fashion.
1841		‘The Irish Duel’ Dublin Comic Songster 153: The when and where was settled fair, / When Pat as bold as brass, / Cried you know what we fight about?
[1846		Westmorland Gaz. 24 Oct. 4/2: I beheld a rat [...] sitting on his hind-quarters [...] either washing his nose or picking a bit of victuals [...] Slaughter-house rats are very bold and brass-faced rats indeed].
1860		Worcester Jrnl 18 Aug. 3/1: When we prance in Rotten Row / [...] / There we scan, bold as brass, / Fast young ladies.
1867		J. Greenwood Unsentimental Journeys 215: Not downcast [...] as you might have expected, but bold as brass.
1876		G. Lander Little Gerty III i: If she isn’t bowlder than brass, I’m a Dutchman!
1882		Cheyenne Transporter (Darlington, OK) 10 Aug. 3/1: Dan came in and says, bold as brass, ‘Well, motgher, I brought a wife hom with me’.
1897		Kipling Captains Courageous 176: ‘Consolation!’ sez he, bould as brass.
1901		B. Pain De Omnibus 28: ‘Picking up a sixpence I dropped just now,’ says she, bold as brass.
1908		Sporting Times 7 Mar. 1/5: He walked into the wine merchant’s office as bold as brass and asked if the purveyor of the juice of the grape could sell him a few cases of Imperial quarts of champagne.
1915		Day Book (Chicago) 1 May 19/1: There was Uncle Thomas walking along as bold as brass, with that creature on his arm.
1922		Joyce Ulysses 340: The twins were now playing in the most approved brotherly fashion, till at last Master Jacky who was really as bold as brass [...] deliberately kicked the ball as hard as ever he could down towards the seaweedy rocks.
1937		J. Curtis You’re in the Racket, Too 138: What are you doing here, if I might ask, lying in bed in my house, as bold as brass?
1955		P. White Tree of Man (1956) 75: We was settun eatun our little pies, when he becomes as bold as brass.
1967		N. Dunn Poor Cow 75: I jumped up a mile as if a bee had stung me – then up I get bold as brass.
1982		P. Bailey An Eng. Madam 57: Then he said, bold as brass: ‘Meet me later on at the main entrance. I finish at eight.’.
1998		J. O’Connor Salesman 337: The little pup was casually strolling down the main street of Dalkey now, bold as brass, and wearing my overcoat!