We Londoners come better prepared for a visit to New York than most US citizens.
You see, we've also got a vast and ever-growing multicultural population, simultaneously too many and not enough airports, a historic but obsolete global sea port, a gargantuan and creaking subway network, a huge reliance on financial services and more than our fair share of crazy people.
But nothing can ever fully prepare you for some of the stuff you come across in NYC.
There's something about the place that engenders an amazing overconfidence and freedom of expression in some of its inhabitants. I suppose it's their way of dealing with the extraordinary demands of that great city.
Late last month I was walking east along 34th Street near Penn Station, wading through crowds of lunchtime shoppers when half a block ahead I saw a placard held up above the heads of the pedestrians. There would be nothing strange about this if it was pointing the way to the nearest branch of Subway or McDonald's or a sale of golfing equipment, but this sign was different.
For confronting the massed humanity of 34th and 7th was an 8ft-high, hand-painted exhortation to "F**k Trump!"
Every 10 seconds the sign would be flipped to reveal the message: "Homeless. If you like my sign give me 25¢. Photos 50¢."
Being an alien neutral observer on the political front, the sight made me laugh (for the sake of balance it could have said "F**k Hillary!" and would have produced the same effect).
I'd never seen such humour, ballsy bravado and enterprise all rolled into one and with a wry smile pulled out my smartphone to record this "only in New York" moment.
At this point the owner of the sign practically assaulted me, thrusting his begging cup in my face, screaming: "Hey, no money, no photo!" so close I could smell his breath.
I limply replied that I'd be good for the money if only he would stand still and let me take his picture. He wasn't having any of it and was now practically foaming at the mouth.
I was offended that he wouldn't trust me. He was calling me a liar. My inner New Yorker triggered and I said: "Well I don't want your picture now - F**k you!" and stomped off to a volley of unrepeatable expletives from my homeless host.
Mine was just one of the many such foul-mouthed collisions that occur 10 times an hour on most Manhattan street corners.
Later on calmer reflection I felt sorry I hadn't just sucked up the slight and given the guy his 50 cents. But it was too late - I was miles away.
How had he blown it? I'm a Londoner and a hard sell for street donations. He had me in the palm of his hand and then suddenly snatched defeat from the jaws of victory.
What got my dander up was that he wouldn't trust my word.
The insurance lesson is clear as day.
It doesn't matter who you are and it how strong your sales pitch is, if you can't operate under the sacred vow of utmost good faith, your customers will desert you and your business will be a failure.