We all know the first rule of Fight Club. And the second rule. This rule also applies to fashion, at least for professional women.
In her interview in the Sunday Times Theresa May broke the rules. She talked about fashion. Openly.
A whole debate may have sprung up around so-called 'Trousergate' - Nicky Morgan criticising Theresa May for wearing £995 leather trousers before being photographed herself carrying a £950 Mulberry handbag - but this is more than just political needling founded on Brexit divisions.
This is something much more deep-rooted and I imagine resonates with every professional woman who knows that what they wear is important but also knows that if they have an interest in fashion they'd be taken more seriously if they kept it to themselves.
I worked for almost 14 years in the City and progressed some way up the ranks. Choosing what to wear was often a dilemma.
In a corporate environment a woman needs to convey professionalism, status and identity - and all without looking like she hasn't spent too much time thinking about it.
There are explicit rules (no denim, for example) but there are also unwritten codes - modest necklines and hemlines, the importance of sleeves, nothing too tight or diaphanous and careful with colour.
It is also important to dress in a way that proclaims a distinction from secretarial and other administrative staff. Professional women want to enter any office or meeting room without anyone even considering that they're there to take notes or make the tea.
I have no doubt that walking on to the trading floor with a copy of Vogue would have sounded the death knell for my career. It wasn't my first choice of reading material but, regardless, it wasn't an option.
And we all know the reason why - it's because there's a commonly held view, especially in corporate environments, that fashion is frivolous, superficial and only for airheads.
Facebook CEO, Mark Zuckerberg, once stated that he wears the same outfit everyday because "I feel like I'm not doing my job if I spend any of my energy on things that are silly or frivolous about my life".
For the Prime Minister and the ultimate corporate woman Theresa May it's a tough call. In many ways she has to walk a tightrope. She needs to be seen to be supporting the British Fashion Industry which, according to the British Fashion Council, is worth an annual £66bn. At the same time she can't be seen to care too much about what she wears.
Most high profile female politicians have steered clear of the debate with some not even alluding to fashion. Hillary Clinton once famously batted away a question on who were her favourite fashion designers.
Angela Merkel is another who avoids the topic entirely. She has been regularly criticized for her choice of clothes but never responds.
Out of the more obviously style-conscious, high profile political women it is worth noting that Christine Lagarde has only made passing mention of her wardrobe.
There's been reference to Michelle Obama and Samantha Cameron's political fashion credentials. However, the difference here is that neither has occupied an elected public position and so is not judged in the same way.
People may also refer to Amal Clooney as a professional woman who clearly has an interest in fashion. But, again, she doesn't talk about it. In fact, she made a clear point of doing the opposite when a reporter once asked her what she was wearing.
There is no doubt that there are double standards at play here. No one pays much attention to what male politicians wear let alone the cost (even if what some wear is expensive). Men are simply not subject to the same level of sartorial scrutiny. A suit is a suit is a suit.
One of the key differences of the Theresa May photo shoot was that she was photographed in a 'high fashion, off-duty look'. This is something that is rarely seen of senior-ranking female politicians. Finding an image of Christine Lagarde (as IMF head or during her time as France's Finance Minister) dressed as though she is going anywhere other than to work is not easy.
I find the debate to be of particular interest because after a long career in the City I left to set up a professional womenswear brand - Rose & Willard.
I did it because I struggled to find appropriate clothes for work. When I say appropriate I mean clothes that tick the boxes above but are also practical - specifically, washable and crease resistant. The idea was to offer women practical solutions to the problems I once faced.
When I tell people I have my own womenswear brand I get the impression that they think my sole interest is in clothes and by extension, fashion. I don't think of myself as being in fashion. Rather I consider myself to be in business. But that's rarely what people register.
Recently I attended an event on 'Imposter Syndrome' which was attended mostly by women working in the City. I got speaking to a woman and swiftly the "what do you do?" question arose. I told her I had my own womenswear label. I could tell she was judging me by fashion metrics, i.e. I'd just been put in the fluffy category. The fact that I owned a company seemed irrelevant.
I then found myself quickly following up with, "I used to work in the City as an equity research analyst". She responded more positively to this but I still had the sense she now saw me as someone who had dumbed down.
I have to admit that I was quite disappointed, more with myself, for needing to certify that I'm not stupid.
Overall it will be difficult to divorce fashion from its ditzy reputation
Theresa May has either begun a discussion which will liberate professional women who feel they can't talk openly about clothes and fashion or she has done herself a disservice. I suspect she's done a bit of both but more of the latter.
She's opened herself up to being associated with something that's not considered serious and this will leave her open to jibes.
Until fashion becomes a debate for men, it will be relegated to something that is trivial and, I suspect, many professional women will continue to dodge the subject in order to avoid being 'reduced' to their clothes.
But I expect the debate will turn. These days most men wear suits to work. On dress down days they just take off their ties. But that is changing. Dress down is becoming more commonplace and at the same time many men are becoming more conscious of what they wear (as seen by growth in the men's fashion market now outpacing women's).
Technology is going to be a major driver of change in the future. I expect the emergence of more technology companies will even change how we dress - less formality, less constriction and fewer suits. As this happens and men have to more consciously consider their wardrobe the debate around the message people send by what they wear may become more serious.