To rinse”, I am told, is millennial-speak for “to make a fool of someone”.

Thus, BuzzFeed’s headline in response to SNP MP Mhairi Black’s conference broadside at the Labour of the Opposition. Parliament’s youngest MP, it declared, “just completely rinsed Jeremy Corbyn”.

Well, up to a point. Though delivered with the panache one has come to expect from Black, the substance of her speech was a different matter. Comprising a series of Nationalist tropes familiar to any Twitter user, it’s easy to “rinse” someone when you don’t give a hoot for consistency or rigorous analysis.

But the fact the Paisley MP devoted a chunk of her speech to attacking the Labour leader spoke volumes about Black’s political backstory and her party’s frantic repositioning in the wake of June’s general election which – as speaker after speaker reminded us last week – the SNP still “won”.

Famously, in her 2015 maiden speech, Black said it was “the Labour Party that left me, not the other way about”. Now quite how Labour managed to “leave” someone born the year Tony Blair became leader has always been a puzzle, but the then fledgling MP went on to explain that independence was actually all about providing an alternative to “the Thatcherite neoliberal policies” propagated by Westminster.

What, then, was Black’s response when, a few months later, the veteran left-winger Jeremy Corbyn became Leader of the Opposition? A mea culpa and an application join the Labour Party? Not a bit of it. Rather, there was a subtle recalibration, Black saying she now supported independence due to the “democratic deficit”, another political argument that preceded her birth by several years. As the Labour MP Gerard Killen Tweeted sardonically: “I never left Mhairi Black, Mhairi Black left me.”

Black’s switch from “utilitarian” to “existential” nationalism was, of course, necessary for her to retain political credibility, Labour’s apparent hopelessness being the whole basis of her remarkable career. But that was back when the SNP joined the chorus about Corbyn being unelectable; now he’s riding high, he requires a conference rinsing as well. So, after weasel words about having been “heartened” when Corbyn became leader, Black declared herself “so disappointed” in him, having done “nothing more than talkin’ a good game”. Oh, the irony.

Corbyn, furthermore, was guilty of spreading “fear and utter drivel” about an independent Scotland suffering from “turbo austerity”. One might have expected such an attack to be followed by an explanation of how Scotland would escape further austerity with £13 billion pounds less to spend each year, but then that would have involved some intellectual heft.

All Black could offer was another Twitter trope. “Why would Westminster want to keep us”, she asked rhetorically, “if we were genuinely a financial burden on the purse strings of the United Kingdom?” One sensed that an additional paragraph about whisky export tax and secret oil fields had ended up on the cutting room floor. “The real question,” added Black, “is can Scotland afford not to be independent?”

Had, of course, Corbyn supported independence after becoming Labour leader, offered to make Nicola Sturgeon Deputy Prime Minister in the interim and copied the SNP’s manifesto word for word, Black would still have ended up “rinsing” him before adoring delegates at the SEC, for Corbyn represents a direct challenge to the SNP’s conceit of itself as a “principled” left-of-centre party.

Indeed, the First Minister set him up to fail within seconds of his election as leader back in September 2015. If Labour, said Sturgeon at the time, could not “quickly demonstrate” it had “a credible chance” of winning the next UK general election, then “many more people in Scotland” were “likely to conclude that independence is the only alternative to continued Tory government”.

Well it wasn’t quick, but arguably the result a few months ago demonstrated precisely that, while the second part of the SNP’s prediction has, disappointingly for them, failed to transpire. Instead, quite a lot of independence supporters have reached the opposite conclusion, that a left-wing Labour government in the UK as a whole offers a more immediate route to progressive governance than another referendum.

And despite all the self-congratulatory rhetoric at the recent SNP conference, the party is clearly worried about that, particularly about the dozens of (Westminster) seats it might conceivably lose to Labour at another “snap” general election, or in 2022. The Programme for Government was evidence of that, as was a gathering in which delegates were encouraged to vent their spleens against the Ministry of Defence and House of Windsor in deliberately meaningless debates.

Then there’s the SNP’s sudden conversion to higher taxes, something considered anathema as recently as the 2016 Holyrood election campaign. Now, with Corbyn’s Labour Party breathing down the Nationalists’ neck, that year’s manifesto pledge to “freeze the Basic Rate of Income Tax throughout the next Parliament to protect those on low and middle incomes” now appears to be up for grabs, although there’s more wriggle room when it comes to the higher rate.

Independence has never been about flags, or borders, or nationalism, or thinking we’re better than anyone else,” claimed Mhairi Black last week, “that narrative has been deliberately created to minimises the appeal of a diverse, brilliant movement that fights for a better future.” That, in a nutshell, is the central conceit of modern Scottish nationalism, and one that finds a Corbyn-led Labour Party rather hard to stomach.

“They,” said Black of Labour, “are what we must never become”, imploring the SNP, in a further loss of irony, to “reject the career politicians [and] cheap slogans”. I have news for Parliament’s youngest MP, her party got there some time ago, and it’ll take more than a rhetorical “rinse” to recover its electoral mojo for as long as Jeremy Corbyn remains the UK’s alternative Prime Minister.