When someone is bold as brass, it means they’re confident to the point of being impolite and disrespectful, and sometimes beyond that point.
In the Daily Mail edition of June 4, 2016 the Tatler Tory Scandal was the subject of the article, “Tatler Tory’s Threats At Baroness’s Carlton Club Drinks Party.” Written by the Political Editor for the Daily Mail, Simon Walters, it addressed the claim that David Cameron’s election aide, Mark Clarke, had, among other things, caused an uproar at a party hosted by Baroness Pidding on September 7, 2015. The idiom was used by in the quote from Paul Abbott, the chief of staff to former Tory Party Chairman Grant Shapps.
Mr. Abbott said Clarke had ‘walked up to her [the guest], bold as brass, and threatened her, saying he knew the names of at least two CWF volunteer who had made complaints [against Clarke to the Tory HQ inquiry].’
Part VII of “The Baby’s Grandmother” by Scottish novelist L.B. (Lucy Bethia) Walford (17 April 1845 – 11 May 1915) was published in the Edinburgh Monthly Magazine (Volume 135) of April 1884. Ms. Walford wrote forty-five books, most of them light-hearted domestic comedies, including this one. The idiom was used Part VII as follows.
“Oh, it’s all right, ma’am, it’s quite within the limits, I believe,” rejoined Mr Tufnell, who had learned much within the last half-hour; “it took me rather aback, I own, at the first blush, but — well, well, we must not be too particular to-night. And to return to Miss Juliet Appleby –“
“And not a bit ashamed of herself!” murmured the lady, still dubiously scanning the gay vivandière, “skipping and twirling as bold as brass.”
“Eh? What?” cried her companion, pricking up his ears. “As bold as brass, did you say? Who’s as bold as brass?”
“That flibbertigibbet Mary –“
Just as with the word cattywampus, the idiom bold as brass was used in Charles Dickens’ book, “The Life and Adventures of Martin Chuzzlewit.” Chapter 27 (where the idiom appears) is prefaced with this statement: Showing that old friends may not only appear with new faces, but in false colours. That people are prone to Bite, and that biters may sometimes be bitten.
‘Why, you’re as bold as brass!’ said Jonas, in the utmost admiration.
‘A man can well afford to be as bold as brass, my good fellow, when he gets gold in exchange!’ cried the chairman, with a laugh that shook him from head to foot. ‘You’ll dine with me to-morrow?’
‘At what time?’ asked Jonas.
‘Seven. Here’s my card. Take the documents. I see you’ll join us!’
‘I don’t know about that,’ said Jonas. ‘There’s a good deal to be looked into first.’
‘You shall look,’ said Montague, slapping him on the back, ‘into anything and everything you please. But you’ll join us, I am convinced. You were made for it. Bullamy!’
George Parker’s book “Life’s Painter of Variegated Characters in Public and Private Life” published in 1789, appears to be the first published example of the idiom.
“He died damn’d hard and as bold as brass. An expression commonly used among the vulgar after returning from an execution.”
In the 1570s, a person who was without modesty and who showed no shame for bad behavior was called brass. Boldness wasn’t included in the description of such a person, but obviously someone without modesty and without shame would be perceived as being bold in their bad behavior. What this means is that for at least two hundred years, some people were bold as brass but it wasn’t expressed that way in print until 1789.
Historically Speaking 