Criticism of what people wear to black-tie events tends to focus on obvious sins: wearing a lounge suit, wearing a coloured tie and wearing a long tie instead of a bow (though this is less objectionable than one may think). These are some of the biggest sins against the traditions of the dinner outfit, and stand out as such. They also stand out because they are committed by a relatively small number of people.

For that reason, I don’t think they are the greatest black-tie sins. They’re big, but they’re rare. More important are the small sins committed by almost everyone. Those demonstrate how disconnected the ensemble is from its traditions, despite the apparent uniformity on display.

Sin 1: Cover your waist

Every black-tie outfit needs to cover the waistband of the trousers in some way. That is an indisputable fact. This covering can take one of three forms: a waistcoat, a cummerbund or a double-breasted jacket.

A waistcoat should be the standard. If you’re wearing a single-breasted dinner jacket, something needs to cover up your shirt – particularly if the jacket only has one button.

A shirt with a stiff, oval front makes this obvious: only the stiff part is meant to show, the rest is covered up by a waistcoat. But even a soft-fronted shirt needs a covering. Even though its pleats form a rectangle on the front of the shirt, and even though they go all the way down to the waistband, that waistband must be covered.

This waistcoat can be black or white. White is less common and more formal, echoing as it does white tie or full fig. It can also be full or backless. If white, it should be made of the same Marcella as the shirt front. If black, it should be the same wool as the trousers.

The cummerbund was invented in the subcontinent as an alternative to the waistcoat for hot weather. It was originally a sash simply tie around the waist.

But what proportion of men at a black-tie event have some form of waist covering? Twenty per cent? Fifteen even? That’s why it’s the greatest sin.

Sin 2: Notch lapels

Most suits have notch lapels; dinner jackets should not have them. At some point, the black-tie industry forgot, or simply got lazy, and conflated the two.

A peaked lapel is more formal, aggressive and rakish. It suits black tie where it wouldn’t suit the decorum of day-to-day business. All dinner jackets, single or double-breasted, should have peak lapels. Yet a significant number (40%? 45%?) of men at a black-tie event will have notch lapels.

(Eagle-eyed readers will notice that my own velvet jacket, worn as black tie, has notch lapels. What can I say? My wardrobe is far from complete and the jacket was a vintage piece to trial a look. It’s on the list to upgrade.)

Sin 3: Shoes

The best shoe to wear with black tie is a patent pump with a grosgrain bow. Second on the list is a patent Oxford. Third is a plain black Oxford, without brogueing and preferably wholecut. All three are acceptable but are less impressive further down the list.

Yet how many men wear pumps? Probably zero. How many patent Oxfords? Perhaps 10%. And of the remainder wearing black leather shoes, there is probably a healthy chunk (again, perhaps 45%) wearing brogues, Derbys, boots or monk straps. So another low-level but popular sin. Multiplying number by grade of sin makes it a greater offence than a long tie.