So far, President Trump's engagement with the British royals has gone well, without a major protocol faux pas. His white-tie getup? Not so much, especially on Twitter where his many critics have added fashion sneering to their arsenal.

Why did it seem so ill-fitting, wondered Twitter users. Why was the waistcoat so long? Were the pants too wide, the tail coat too short? Some critics took similar pokes at his sons, Donald Trump Jr. and Eric Trump.

The president, who has been mocked for his baggy fashion sense ever since his inauguration (remember that too-long red tie?), did not look entirely comfortable in his white-tie outfit for Monday night's state banquet at Buckingham Palace hosted by Queen Elizabeth II.

By contrast, the British guests at the glittery dinner in the palace ballroom looked as if they had just wandered off the set of "Downton Abbey."

The sartorially-adept royal men, such as Prince Charles, Prince Andrew and Prince William, have regularly worn white-tie over the decades – they know what they're doing, and more to the point, so do their tailors.

So Trump's fashion foes on Twitter, already loaded for bear about him anyway, let loose.

"I have never seen anyone make a white tie & tailcoat look so sloppy," sniffed RiotWomenn.

Trump was compared to a cartoon character and even Frankenstein.

"OK, I was gonna make a joke about how Trump looks like the bit from Young Frankenstein, but, honestly, that's unfair to how well tailored the Monster's tux is," tweeted David J Bradley.

Maybe white-tie trends have changed? But no, wrote Jonathan Evans, the digital style director for the men's magazine Esquire. He says Trump's version was just wrong, most obviously in that the white waistcoat hung below his tailcoat.

"Donald Trump's outfit. It just isn't right...right? It's not easy to put your finger on the exact cause of the problem, but you don't need to know the ins and outs of white tie to know that something is not right with this situation," Evans wrote.

"Trump's ties are way too damn long, reaching well past his waist. You can't do that with a bow tie. But you can make a vest that's too long, and probably for the same reason as the ties: vanity, and the mistaken belief that a longer-than-average element around the belly distracts from Trump's girth."

As a comparison, check out Steven Mnuchin, the U.S. Treasury secretary, who accompanied Duchess Kate of Cambridge into the banquet (she was in a diamond tiara and a white Alexander McQueen gown of cascading ruffles). Mnuchin's tux looked perfect – or at least familiar.

Trump's sons' tuxes looked better than Dad's but they still came in for some mocking. One user posted a picture of the younger Trumps (Donald Jr., Eric Trump and his wife, Lara, Ivanka Trump and her husband Jared Kushner, and Tiffany Trump) even wondered if there was something wrong with Eric Trump's leg.

"They look awful," commented 3ChicsPolitico.

One mocker used the tuxedo issue to take a shot at Trump's much-derided claims of being a billionaire – claims that have been put in doubt by a recent report about his taxes showing his businesses lost more than $1 billion over a decade.

"The fact that Trump doesn't own a tailored tuxedo is the ultimate proof that he's nowhere near as rich as he claims," tweeted pajama_patty.

On the other hand, Trump admirers sneered back.

"I find it funny that the same people who think this getup is stylish and appropriate are criticizing President Trump’s tuxedo in the UK," tweeted Tom Bostedt over a picture of man in a stylish, close-fitting British-style striped suit.

Meanwhile, first lady Melania Trump, a statuesque former fashion model, looked as impeccable as ever, whether in dresses designed to pay tribute to her hosts or in her Dior Haute Couture ivory silk crepe gown with silk tulle detail that she wore to the banquet.

Evans of Esquire had some advice for Melania's husband.

"Donald, get a new vest. Maybe head to Savile Row. It's right there in London, and the heart of England's generations-old tailoring tradition. The folks there might even be able to tell you what size clothing you should wear," he wrote.

"Because it's pretty clear you have no idea."

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