"Mr. Johnson is not a politician. He is an act," wrote his Telegraph colleague Simon Heffer in the run-up to the mayoral contest. "For some of us, the joke has worn not thin, but out."
And Heffer's comments were mere playground banter compared with some of the barbs aimed at him from The Guardian, for whom the prospect of a Johnson mayoralty was deemed the stuff of darkest nightmares.
Columnist Polly Toynbee branded him "a jester, toff, self-absorbed sociopath and serial liar", while for Zoe Williams he was "a bigoted, lying, old Etonian buffoon". The same paper also ran a quote from fashion designer Vivienne Westwood, who memorably declared on the radio: "Boris as mayor? It just exposes democracy as a sham."
Sitting at the head of a vast boardroom table in his sun-flooded City Hall office, Johnson, 44, splutters with laughter when he hears the last comment. "Did she really say that? I'm... you know... I'm a firm believer that, you know..." he begins unpromisingly. "Obviously, I love journalists and love journalism and people have got newspapers to sell, points of view to make and attitudes to strike, and they've got to get on and do it, and quite right too." He slaps the table, grinning. "Democracy would be the poorer without it. It's a privilege to be written about in The Guardian!"
Now 100 days into his new role - a job he claims he has taken to "like a greased bounding panther" - Total Politics asks him to name his proudest achievement and biggest blunder so far?
"Oh boy, um," is Johnson's opening gambit, making him sound rather more like a lethargic Bagpuss than the aforementioned panther, greased or otherwise. "My proudest achievement is to have brought to City Hall a pretty diverse team of talents, many of whom were broadly Conservative and they've taken over seamlessly the running of London. They've understood that the priority for us - and I think for the next Tory government - is tackling deprivation and disadvantage."
He pauses. "And let me think of a mistake for you. The most disappointing thing was um..." A smile creeps over his face, as he jabs a finger over my head. "That wine store... [Ken] Livingstone's wine store... I was thrilled to find it, but it turns out it's all owned by the taxpayer and I can't even drink it. If I pour you a glass of Livingstone's Chateauneuf-du-Pape, I'd have to fill in some sort of form..."
This is Boris Johnson. One moment he's deadly serious. The next he's Boris the Clown. What, I ask, has he found most surprising about the job? "How big it is. I'm in government. This is government. This is government. This is big. This is huge. Huge, huge. This is bigger than my last job as a shadow spokesman by a factor of a hundred thousand."
It doubtless dawned on him just how big the job was during the firestorm surrounding the resignation of his deputy mayor for young people, Ray Lewis. Less than two months into his tenure, youth worker Lewis quit in disgrace amid allegations of past financial and personal misconduct.
The event became a national story, bringing Johnson's City Hall honeymoon to a juddering halt. But when his chief of staff, Nick Boles, took full blame over the failure to vet Ray Lewis, some Tories were outraged at the way Johnson had dodged responsibility, given that it was his decision to appoint the youth worker in the first place.
"Of course [Lewis was my appointment]," he concurs. For a moment I think we're in for an ‘on-message' answer, but soon Boris is camping it up again. "It's outrageous. And Nick has no right to take the blame. I take it back from Nick. I don't want him running off with the blame like that. I condone these acts of blame theft. No, I condemn these acts of blame theft by Nick. And I'd like you to know I take responsibility for what happened, of course I do."
A long pause. Suddenly, he's serious again. "But the ideas that Ray has are very good ones and we will pursue them."
The Lewis debacle would have been manna from heaven to Johnson's predecessor and arch foe, Ken Livingstone. Is there any truth in the press reports that the ex-Mayor has become a regular visitor to City Hall, where he is said to watch Johnson from the public gallery? "Yes, he hangs around like a sort of brooding pterodactyl and he's very welcome to do it," confirms Johnson. "Honestly, this is a wonderful job, it really is the best in British politics. But I have no official opposition. I've got a Labour party in meltdown and it's good that there's someone in London who's there to fire off press releases saying what a tosser I am, which he does virtually every day."
It's not difficult to see why Livingstone bears a grudge. During the fractious campaign, his administration was repeatedly accused of sleaze and cronyism.
But just what exactly did Johnson's team - and his Forensic Audit Panel - find when they got their feet under the table?
"Don't forget there are six or seven police investigations going on, some of which will almost certainly lead to prosecutions," he says.
"I think parts of Ken's regime, or parts of the immediate vicinity of his regime, had become pretty sleazy, or very sleazy indeed. I don't for one minute think Ken was personally corrupt, but it's like any bunch of guys who've been around too long. I think they were very, very casual with public money and they were reckless in the way they spent it. The worst thing they did was undermine confidence in the ability of this body and particularly the London Development Agency to manage public money."
How Johnson manages spending - and cuts out waste - will be watched carefully by the media, much of whom view his stint at City Hall as a testing-bed for a future David Cameron administration in Downing Street. To that end, goes the conventional wisdom, every move ‘Team Boris' makes is being choreographed by Tory central office. "Bollocks!" replies Johnson, miffed at the suggestion. "In order to make the story nationally relevant and thereby get it on the news agenda, journalists have to find some sort of read across [between City Hall and central office]. The reality is we're working flat-out for London."
Then, he adds, tellingly: "But obviously I'm hopeful we'll do some things which will show that compassionate Conservatism can work in London and therefore can work in metropolitan areas across the country."
How often does he speak to Cameron? The mayor mumbles for a moment before reaching for his mobile phone. "You know... I... Shall we call him now?" he says, scrolling for his boss's number. But as he clamps the phone to his ear, he remembers something. "Ah, he's on holiday! I can't ring him. Poor chap, he's on holiday!" Do they speak on a daily basis, I ask again? "No, no, we talk from time to time," he says, cagily.
In his coruscating article, Heffer went on to describe Johnson as "the most ambitious person I have ever met", who will regard the mayoralty as "a stepping-stone to a Cameron cabinet." Indeed, when quizzed by Piers Morgan in GQ magazine a year ago about whether he wanted to be PM one day, Johnson replied - tongue, perhaps, in cheek - "Well, of course. In an ideal world."
So does he still harbour ambitions for the top job? He bumbles and brays, before paraphrasing Thatcher's nemesis Michael Heseltine. "Look, I really cannot foresee the circumstances in which I'll be called upon to serve in any such office," his eyes gleam mischievously. "Honestly, my appetite for power is glutted."
We'll take that as a maybe then. But if he does hanker after Downing Street, he'll have to cut down on the gags first.BORIS JOHNSON: QUICK-FIRES
JS: Which song gets you on the dance floor?BJ: Start Me Up by the Rolling Stones.
JS: Are you, like the PM, a fan of the Arctic Monkeys?BJ: Do you know, I... (Starts singing I Bet You Look Good On The Dancefloor in a poor Northern accent). I don't think they're as good as they're cracked up to be... I'm probably going to lose myself about a billion votes... but are they really that wonderful?
JS: What about your boss's old favourite, [rapper] Dizzee Rascal? BJ: No... Um. (Mumbles)JS: No plans to invite him to City Hall?BJ: No, but I tell you who [sic] does. [US rapper] Kanye West is going to do something for us.
JS: Favourite TV show?BJ: Er favourite TV show? Cripes... Um.
JS: Favourite movie?BJ: Favourite movie's easier... (Pauses) I'd say Apocalypse Now, probably. No, no Jaws. Favourite TV show. Um. God. Name a good one?JS: The West Wing?BJ: No!JS: Too leftwing for you?BJ: (laughs) Is it leftwing? It's unbelievably boring. JS: I dunno, The Sopranos? I'm not giving you the answers.
JS: Which actress/movie star did you have blue-tacked to your wall at school?BJ: Ah! Um. I didn't because I was, I was... Um. [American model] Cheryl Tiegs! Do you remember Cheryl Tiegs? And the tennis girl. The Athena tennis girl [poster]. And I'll tell you this much for free. On the whole I was in favour of the blonde one rather than the dark one in Abba, but it was a close-run thing.
JS: Your favourite view anywhere in the world? BJ: (Nods at the window) From this window. Look at that!
JS: Earliest political memory? BJ: Um. Oh God. Wait a moment. Yeah. Jesus, what was it? Let me just think. This is a question which deserves... Obviously I remember lots...JS: [Shadow foreign secretary] William Hague giving his famous party conference speech?BJ: (Mimics Hague's Yorkshire accent) That was when I was at school. I was at prep school. Ah yes. I was 11 or 12.
JS: Which six people, living or dead, would you invite to your perfect dinner party?BJ: Oh yes. This is easy. Scarlett Johansson. Um. Scarlett Johansson. Um. You know. Um. Can we stop with her? Um. Pericles... Scarlett Johansson, Pericles and Shakespeare...
JS: Is character more important than personality?BJ: They're the same thing, aren't they? ‘Ethos anthropoi daimon', ‘Character is destiny'.
JS: Tony Blair or Gordon Brown - if you had to choose one...?BJ: (A touch sheepishly) I'm afraid I miss Tony a bit.