It's not the done thing for news presenters to expose their personal feelings about a story. Especially while they're introducing it on The News.
We knew Donna Traynor wouldn't come out of a clip of Jordan showing off her new baby asking 'Is there anyone left in the UK who gives a cat's ass?'. Just as we accepted that Huw Edwards wouldn't preface this week's grievous revelation of David Cameron's sore back with 'Here's political editor Nick Robinson on a story which has left most of the country overwhelmingly indifferent and wondering who makes the decisions about what makes headlines'.
No, we expect our news readers to be objective harbingers of world events, open-faced and opinion-free even when they're delivering reports of some of the most grotesque acts and loathsome human beings on the planet. Even a tiny 'Yay!' at the egging of Nigel Farage would be impermissible, despite it obviously being a Good and Funny Thing.
There is an exception however, as this week has demonstrated. It occurs when the subject is a pop band loved mainly by teenage girls.
It's the done thing for middle-aged men to premise coverage of said band with rolling eyes, an amused smirk or an introduction along the lines of 'I have to admit, this isn't something I know anything about'.
That's code for, 'my editors think that record-breaking crowds for a London film premiere about the world's biggest pop band is newsworthy, but I want it to be known that I myself am above such trifles and hope my sniffy condescension will prove it'.
There are few social groups more openly derided by the respectable media than teenage girls. This is an arena in which classes and races are rightfully treated equally. Sub-groups which used to be considered joke fodder, such as football fans or geeks (Apple and Doctor Who sorted that out) are now indulged with warmth. I welcome that. But it strikes me that radio and TV journalists feel free, even compelled, to undermine things loved by teenage girls, who, when presented as a group, are often portrayed as stupid, hysterical lunatics.
Thus have global superstars One Direction (30 million record sales, number one in more than 30 countries) suffered this week, when the premiere of their on the road film This is Us brought Leicester Square to a standstill.
Harry Styles makes teenage girls scream so, as thousands of grown-ups on Twitter and Facebook feel compelled to point out, he is obviously a loathsome little twit. NME readers recently voted him their most hated man.
Twitter users, including comedian David Schneider and the band Reverend and the Makers, sent viral a mock poster of the band calling them 'completely talentless s**** trumpets' who were being used to exploit 'teenage girls and the mentally challenged'. Yes, the two are often regarded as interchangeable by people who have no experience of being either.
I don't know if this is about jealousy of cherubic boys who rouse passion in creatures whose elusiveness once caused these men such agony, or if it's just a thoughtlessly unpleasant attitude to young women tussling with the wholly natural dips and crescendos of teenage hormones.
Actually, the band seem rather likeable and honest and, in Styles and Niall Horan, smart and self-deprecating. They're making the most of the times of their lives. What fool wouldn't? It's the frothing-mouthed disparagers I worry about; just what bitterness or emptiness drives their eager hatred?