He was crushed when all Warhol had to say was: "I like your yellow shoes."
It's an anecdote that kept resounding during the grand opening of the big, shiny, fabulous new Warhol exhibition at The MAC last night.
Most of the prints, posters and reproductions on display found Warhol (right) elevating the everyday to the status of art, whilst reducing the great and the good to the level of mass produced commodity.
Deputy First Minister McGuinness has come a long way from the war hole of the '70s Bogside to the different kind of revolutionary explosion on display in the MAC.
"Andy Warhol could have been talking about us," Mr McGuinness declared to a huddled audience who for all the world, in the Factory-like multi-layered MAC, looked like well-dressed refugees from a natural disaster.
"It doesn't matter how slow you go as long as you don't stop," he concluded, and simultaneously won the inaugural Chancer's Cup for most tenuous link in a speech ever.
But this was another chancer's evening – a small second generation Slovakian visionary who changed the way we look at the world.
There was much to take in over three floors and as many gallery spaces, as the huddled masses spread out to drink in the sheer Warholian wealth on show, and time and again, it hit you just how long a shadow this tiny, odd man cast over late 20th century culture.
Everywhere the joy of repetition, appropriately enough, repeated itself. Stitched monochrome photographs on paper of no parking signs and brunch menus were made sexy by replication. Giant 'silver clouds', aka helium-filled balloons, even reduced one MLA who shall remain known as Anna Lo to fits of girlish playfulness.
By the '80s, popular culture had caught up with Warhol's notion of commodity and art being pretty synonymous. Looking at his double giant hamburgers from '85-'86, you realise the likes of Ronald McDonald had cottoned on to the consumerist iconography schtick, as Andy almost certainly didn't call it.
A portrait of Lenin made in the final year of Warhol's life has him as a shadowy figure, receding into a darkened backdrop. It's in stark contrast to the series of earlier Warhol portraits such as Mao in lippy and of course eight Elvises – sadly not on display last night, on account of being flogged for £100m a few years back.
But then you noticed that this dark portrait loaded with a sense of mortality was hanging on a wall adorned with bright yellow painted cows.
Ultimately the power of these pieces isn't in the wonder of the craft, it's that they're all charged with the electrifying essence of his greatest creation – Andy Warhol.
And it's maybe intriguing to wonder what the artist who cultivated fetish from the everyday would have made of a country where an iconic flag was converted into an emblem of irrational passion.
Warhol's most lasting legacy on popular culture wasn't through prints and portraits on walls, or even in his often unwatchable films.
The MAC may have captured something of his essence, but really, Andy's babies are out in the streets, department stores and singing in front of a mirror.
Everybody is indeed now famous for the 15 minutes he once mischievously predicted.
It's good that we've finally given Andy his first 15 minutes in a city so inadvertently in thrall to his legacy.