The Oscar Nominees Lunch proves not even stars know what "smart casual" means.

Nothing strikes more fear into a person than an invite marked with the dress code “smart casual”.

It’s the fashion equivalent of walking across a minefield.

Will it be the kind of place where they really mean “smart but not quite a ballgown”? Or do they really mean “casual-but-not-pyjamas-you-slob?”.

For something so seemingly harmless and informal, ‘smart casual’ sure causes a lot of angst.

Either way, it's not just us mere mortals who are totally bamboozled by it.

Even celebrities - for whom attending events is basically part of their job - don't have the whole smart casual dress code thing worked out.

Yesterday was the Oscar Nominees Luncheon, a time for all this year's nominees to gather together and celebrate their achievements "informally", with a (you guessed it) smart casual dress code rather than the black or white tie of the official ceremony.

Presenting our newest class of Oscar nominees! #OscarsLunch pic.twitter.com/timunCWy4S

— The Academy (@TheAcademy) February 7, 2017

At the end, they gather for a "class photo".

Look closely at this year's snap and you'll notice one glaringly obvious thing that stands out (aside from the lack of diversity in nominees, which is a whole other problem.)

Pharrell Williams.

While almost every other male opted for a classic suit and shirt (smart) without a tie (casual) combination, the musician and producer, nominated for his work producing Best Picture nominee Hidden Pictures, is rocking jeans, a slogan sweatshirt and a baseball cap.

Clearly, he went more heavy on the casual.

The Academy Awards nominees gather for this year's class photo at the #OscarLunch. pic.twitter.com/G2bzMnNQov

— Variety (@Variety) February 6, 2017

Unfortunately for the 43-year-old, the simplicity (read: limited options) of menswear means his outfit sticks out a bit like a sore thumb.

Of course, he was probably the comfiest of the lot and certainly didn't look bothered by it. After all, this is the guy who wore an enormous hat that became a viral sensation, a meme and got its own twitter account.

When it comes to fashion, Williams is by no means shy.

There's much more to Pharrell Williams than his big hat. Read our Timeline on the man here: https://t.co/HIFqteIiNK pic.twitter.com/EjmB8lZLql

— Exclaim! (@exclaimdotca) February 2, 2017

Smart casual for women is far less black and white, with female nominees opting for everything from silk jumpsuits (Emma Stone) to jacket-blouse-pants-and-heels combos (Octavia Spencer.)

As a result, it was an interesting and arguably far more relatable red carpet arrival than most. (Post continues after gallery.)

So what does 'smart casual' ACTUALLY mean?

Translated into normal-speak, regard it as relaxed but still well-dressed.

Men can ditch the tie but will probably still require a jacket, with a suit or jacket and trousers combination a safe bet. Unfortunately the general consensus remains: no jeans.

You don't have to be boring, though - a patterned shirt with checks or stripes or pastel colours rather than plain white work well.

For women, the 'rules' are far more fluid. You can still wear the fail-safe dress, but it's also a great opportunity to go for separates like a silky blouse and skirt, tailored pants, a jumpsuit or even a skirt suit (check out Nicole Kidman).

Ultimately though, there's plenty to learn from Williams. The requirement for any dress code? Confidence in what you're wearing.

So if you're feeling like a sequin evening dress for smart casual, do it.

But, say, jeans and a sweatshirt for black tie? You're braver than most.

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