Vincent Hogan in Las Vegas: After the pantomime, reality bites
McCullough believes there can be a shock in the city were dreams are made and broken
"In boxing, everything you hear is a lie!" - Don King
Two bikini-clad girls stroll southward on the Strip, wearing huge, plumed feather head-pieces and smiling solicitous smiles.
One head-piece is coloured red, white and blue; the other green, white and gold. "Hey baby, come and get your picture taken with us," the girls recite in high-shrieked voices to men of every shape and size. "You Irish, honey?"
Across the way, a giant, flashing neon sign above the Rainforest Cafe advertises 'Conor McGregor's after-fight party at the Encore Beach Club'.
The night air here is fevered with commerce, from the big, casino hotels selling their Broadway acts right down to tired, faintly wizened men and women selling ice-cold water on the pavement.
Vegas is open for business, all business.
This is a place, remember, that turned atomic testing into a tourist attraction, one - as Noel Coward put it - inviting "the masses of earnest morons to fling their money down the drain".
The Strip is packed with couples escaping the zombie faith of the casino floors to inhale some hot desert air, hit a show or, maybe, some all-night wedding chapel before re-submitting to the lust for gamble.
McGregor likes people to know how much he feels at home here. So the puzzle is in trying to figure out where the cartoon ends and the father begins. Because the glare has become the show, the nonsense brings the profit.
Doing sit-ups in front of a green Lamborghini, showing up at media events in garish shorts under a polar bear mink that would have made Liberace's furrier blush, forever wearing shades indoors, trash-talking like a rap star, generally just squaring up to the world as if everyone's got a hand in his pocket, all these things feed the billboard creation.
They make McGregor perfect for Vegas and Vegas perfect for him. Take your pick: The Eiffel Tower, the Great Pyramid, Venice's Grand Canal, every Kodak opportunity you could want is on the doorstep here. Nothing is real. Nothing ever needs to be.
So we will get a fight tonight, white man against black. Boxing royalty against a swaggering, brash interloper. Sworn enemies. In box-office depiction, trash-talking representatives of two hard-bitten, dangerous communities. Except, that's not entirely true, is it? McGregor's teenage years were spent with sober, responsible parents in a Lucan semi-detached. True, he had childhood friends who'd fall the wrong side of the tracks, but not him.
John Kavanagh says the trash-talking side to McGregor's personality can be traced back to his earliest days in Crumlin, where, "If you can't give and take a bit of ribbing, you're going to be in for a tough time."
But the rougher edges to Mayweather's story have to be unimaginable to McGregor. He was, after all, never used as a human shield by his father to avoid being shot by a gun-toting in-law. Floyd Mayweather Jr was, the in-law shooting Mayweather Sr in the calf. McGregor's father didn't go to prison for drug-trafficking. 'The Notorious' didn't have the kind of angry, abjectly dysfunctional childhood that made it somehow inevitable that he, too, might end up doing time behind bars.
Just over seven miles north-west of the T-Mobile Arena, where tonight's event takes place, is Clark County Detention Centre, the place Mayweather Jr spent two months in solitary confinement during the summer of 2012 for a domestic violence conviction.
His history with women is a rotten one. In fact, he has faced accusations of domestic abuse dating all the way back to 2002, involving five different partners. Yet, roughly a year before the first accusation, he dedicated a victory over Diego Corrales to "all the battered women in the world".
This week, Mayweather's nights here have - reputedly - been spent in his own gentleman's club, 'Girl Collection', a 7,000 square-foot premises on an industrial area just west of the Strip.
"Women will always be in style," he grins of a business where a bottle of good Cognac can set the customer back $10,000 (€8,400).
Irony, you will gather, has no boundaries in this town.
To the front of tonight's fight venue stands a 30-foot-tall wire sculpture of a voluptuous female dancer. 'Bliss Dance' is the work of Marco Cochrane, celebrating "the power and independence of women". It is elegant and beautiful but, just off the Vegas Strip, you have to suspect it carries the status of a stage-show gag.
So peel away the vulgarity of these past weeks, sidestep the bling, the devotion to hubris, decommission the cartoon in other words and look closely at the two men fighting here.
If you do, you will struggle to see them as having anything much in common, beyond an appreciation of conflict and profit.
As for human beings, Mayweather makes McGregor look like a social worker.
On Thursday morning, Dana White was still doing his PT Barnum thing, selling tickets on the back of an idea that this fight will prove Mayweather's worst decision, that come showtime McGregor will be a barracuda set loose in a giant goldfish bowl.
He dipped between the big TV networks in a black BMW 750 MSport sporting fat, black rims, a look-at-me car in the capital city of kitsch. Fox Sports interviewed him in front of the T-Mobile Arena, ESPN in front of the MGM. White wore a black T-shirt with a boxing ring printed on the front in the colours of the Irish tricolour, above which were the words 'McGregor Boxing Club'.
One of the ESPN guests suggested that a McGregor victory would put the Dubliner in the category of, "someone like say, Bruce Lee".
White seemed happy with the comparison. He agreed that Mayweather losing would constitute "the greatest upset in the history of all sports", yet proposed that, maybe, those who could not see it happen were simply looking at things from the wrong angle.
"You know this isn't going to be a boxing match, it's going to be a fight," he smiled.
"In a 12-round fight, Conor McGregor will catch Floyd Mayweather," said White. "He will hit him. And he's not going to be just looking for the chin, he's going to be looking for the arms, the shoulders, the chest, he's going to hit him everywhere."
On that, there seemed broad agreement. "Oh yeah," guffawed a fellow guest. "I see McGregor hitting his arms and shoulders all right!"
Earlier, on the same programme, Roy Jones Jr - like Mayweather a former multiple-weight world champion - predicted that McGregor would suffer a stoppage. Why?
"If you talk that junk to me, you gotta go!"
Wayne McCullough thought Mayweather sounded tired at Wednesday's press conference, as if the fire in his belly might have gone cold.
He's known 'The Money Man' for more than 20 years, the two having sparred in the late 1990s as Mayweather closed in on his first professional belt. McCullough says he considers his "friend" to be a man broadly misunderstood in popular public depiction, citing his charity work and the fact that he surrounds himself with "at least 50 people he doesn't need".
This week, he reckoned Mayweather was growing weary of the whole loud, uncouth charade that came to constitute the big-fight build-up. Without fans allowed into the KA Theatre, the final press conference acquired an oddly adult, sanitised feel and McGregor seemed disarmed by that.
He'd arrived through the black stage curtain, tailored impeccably as ever and dispensing a faintly Papal wave in anticipation - it seemed - of a rowdy welcome. But the assembled media barely noticed his arrival, only the gentlest ripple of applause following McGregor to his chair.
Then, having delivered a familiarly adversarial prophecy: "I will break this old man", he found himself sitting, listening to an opponent who took to communicating all the violence of Judy Garland on the Yellow Brick Road. Mayweather thanked everybody from God to the founding fathers of Vegas, before calling McGregor "a great fighter".
From the putrid narrative of the build-up, he was all but sending his opponent a love letter.
"That was really strange," suggested McCullough afterwards. An Olympic silver medallist from the Barcelona Games, McCullough has been living here for almost quarter of a century and is familiar with the conventional rhythms of a Vegas fight gathering. Wednesday did not follow those rhythms.
"The truth is reality kicks in the week of the fight," he told me. "But I'm surprised, the fans have been lining up outside and they never let them in. This is the strangest press conference I've ever seen in my life. I've been to (Mike) Tyson press conferences and I've been to some of Floyd's other ones and this was, just, dead.
"It was strange and Floyd looked tired. I've known him for 20 years, he usually wants to be the villain. He wants to sound like he's horrible, but he's not. Today he turned it around. And Conor seemed disarmed because he always wants it to be a bit of a scuffle.
"That could be a mind game, of course. Because he (Mayweather) was really quiet, humble. Face to face, Conor was speaking to him and Floyd was just saying nothing. Conor took his glasses off and he just stood there.
"There was nothing to come back at. He made Conor sound great, didn't disrespect him. Today it was Floyd's stage, it really was."
Of his time sparring with a young Mayweather, McCullough recalled: "When he's on his A game, you think there are three people in with you! He was never a big puncher, but his speed was his power."
So McCullough patently understands the potential implications for boxing in a Mayweather defeat now. It would, effectively, humiliate his sport. He surely cannot imagine that happening?
"Actually, I can yeah," he smiles thinly.
"If Floyd walks out there and drills Conor over and over, stops him in the second round, then it's a win-win for him. But, if it goes 12 rounds, I think Conor will say something like, 'Oh, I came into your sport, it was easy!'. In that respect, if McGregor wins it'll be a bit of a disaster for boxing.
"But I think the age factor could be the thing. Floyd might step in the ring and he could get old. It's a possibility. A fighter can get old in one night. The good scenario is that Floyd goes out there and wins the fight easily and goes home. But that's just a gut feeling I have. I think McGregor can win."
What happens next is, arguably, the least important thing. The money is made. The hype has devoured its market.
Whatever the outcome, McGregor and Mayweather will - most likely - be grown up about things when it's all over. That's how this business works. They'll make as if these past weeks have been some kind of Doctor Gonzo hallucination.
"For a loser, Vegas is the meanest town on earth," Hunter S Thompson wrote in 'Fear and Loathing'. But not this time it won't be. There can be no losers when the money piles so high it's all but blotting out the desert sun.
And this may be where the McGregor story reaches its natural arc. Logically, there is no reason to believe that Mayweather, even on old legs, won't have too much science for the Dubliner's fury. The McGregor achievement has been in getting here, of insinuating himself into the imaginations of a global audience.
He will go to the ring tonight in a Donatella Versace robe assured of a life-changing purse and hardened in his conviction that he represents a generation of people for whom Official Ireland is a stuffy, hostile place.
A generation uninterested in the mores and behavioural orthodoxies of old, in the prescriptive deference to church and state. A lot of people may not like that, but it would be unwise to ignore it.
Conor McGregor is the face of an Ireland that is brash, unapologetic, challenging. An ugly face in some eyes.
His language is routinely crude, casual in provocation and, at times, blind to any adult sense of the fulminating world we live in.
In their final face-off, he delivered a barely perceptible Samurai bow, a gesture Mayweather pointedly turned away from, choosing not to reciprocate. And, after weeks of reckless verbal incontinence, that moment of uneasy silence seemed far more interesting than the hours of puerile, caveman baiting that preceded it.
On some levels, McGregor remains unknowable to us. His psychology is his strength, the ability to create a persona that keeps jumping out at the world from comic book pages.
It isn't in his interests to allow a light be shone behind that persona, not yet at least. So, for now, we are confined to fleeting glimpses of another man, a different story. In an untypically considered interview on Showtime this week, he was asked to explain the phenomenon of 'The Notorious' that seems to have charmed the imaginations of millions.
"People are just attached to this journey, a young Irishman... we're not supposed to be at this pinnacle," he said.
"We are taught that... it's almost shun upon to be this outspoken and this confident and to be in these positions. I think the world has just taken note of this.
"This is a young, confident Irishman that's been on one hell of a journey and they are latching onto it."
Then he predicted that the world would "explode" when he knocks out Mayweather, returning once more to the hyperbole that has made this a virtual billion-dollar fight. And, in a city that sweats guilt, McGregor was sounding himself again: cocky, clear of conscience. The highest-profile Irishman on the planet today.
Promising to shock the world.