And well she might love Manhattan. We are talking at the launch party for a new shop - established with the help of her Japanese backers - in the heart of New York's relentlessly trendy SoHo district. It is her first shop in America. The cavernous room, hung with Swarovski chandeliers to evoke an 18th Century salon with a stage at the rear, where we both now teeter, is heaving with the vain and the beautiful.
The affair is subtly different from most of the other must-be-seen-at parties that happen here on any night of the week for artists, authors, club bandits or whoever. Seen from the stage, the masses tonight do not appear as, for example, the usual sea of fashionable black, although few have dared to outdo Westwood, dressed in ecclesiastical purple, with an all too visible red bodice, platforms and a cheeky spider plunged deep in her cleavage.
More impressive, though, is the reverence for Westwood herself. Regularly ridiculed by British tabloids, Westwood is fashion's most famous femme mechante. It was she who went to receive her OBE from the Queen knickerless and in a see-through dress and who first drew fame with her punk designs in the early 1970s and her collaboration with her then partner and punk- pioneer, Malcolm McClaren. In the industry, though, she is consistently rated among the most-important designers.
And here, on Greene Street, the congregation is adoring. Fans squeeze through the crush on to the stage to meet her and she is friendly back. With some reluctance, she even acquiesces to a young woman's request to autograph her umbrella. Less lucky, perhaps, was the impeccably trendy young man who clambers up beside her to ask for an interview for his fashion magazine. "No, that magazine's pretty awful," comes the reply. "You're all as bad as each other. I don't know why you bother". He retreats.
At 58, Westwood isn't really leaving London, even if Fashion Week will have to do without her for this year at least. She is not sure she can stomach America either. Anti-patriotism is one of her pet themes. "Come to think of it, I'm probably more anti-American than I am anti-British," she muses, before correcting herself. "No, no, I'm more anti-British than I'm anti-American." And she has just bought a large house in Clapham, south London, so she must go back. Then again, there is Alexandra, her dog.
If hype (and Blair) bothers her in London, in New York it is Gap-style clothing. "I think the funniest thing is the name. I mean, hasn't anyone thought about what Gap means - that there is nothing between the ears," she jokes. "Fashion in American is nothing. It's just mass-market minimalism and I think that is responsible for the stagnation of fashion around the world, really".
So how, then, will Westwood's outre designs go down in the home territory of Gap and of conformist, monochrome dressing? Who will buy that straw skirt in the window - one she once wore herself? One doubter is Richard Martin, curator of the Metropolitan Museum's Costume Institute. "The erudition of her work makes Americans very suspicious," he told the New York Observer last week. "Americans look for casualness, simplicity, the classic issue of being modern."
The SoHo shop is no small investment for Westwood and Japan's Itochu Corporation, which, since entering into a licensing agreement with her in 1993, has swelled Westwood's annual revenue from $400,000 (pounds 250,000) to around $10m. All her lines - Gold Label, which is the couture stuff, the more mainstream Red Label as well as her Anglomania and Man labels - will be available in the shop. And, from offices in the same building, she aims to expand in America, perhaps selling through department stores.
The timing of Friday's opening was no accident. On Tuesday she will show her autumn-winter Red Label collection at the New York Fashion Week - the show that would otherwise have been on a London catwalk. "But that decision wasn't really about London itself," says Philip McInnes, who will manage the SoHo shop. "Vivienne wanted to do the show here to help promote the shop and really open up in America.
"She never does anything by half," he says. "She isn't really bored by London. People take what Vivienne says the wrong way. They take it as an insult, when it isn't meant that way."
Back on stage, Ms Westwood predicts that the quality of her clothes will win over even Americans. "We do something no one else does," she says. "We offer a real choice to people. My clothes are the real thing. I do different clothes because I've always refused to be tied to some hype machine."
Might she have been tempted to show off her OBE here tonight, and play up the part of the British eccentric? "Well, actually, maybe I should get the medal out more often. And I do now and again. It goes very nicely with tartan and anything that's sort of military, really."