Susie Rushton: Now I'm pregnant, I see people at their most selfish

It sounds like an edict by a head prefect, from the same rule book as "no running in the corridors". Actually, it's the latest scheme from the Mayor of London, whose policies, priorities and modes of expression suggest he still thinks he's in the upper sixth.

As part of Boris Johnson's "transport manifesto", teenagers in London will be told to "stand up for their elders" – and pregnant women and disabled people – while travelling on buses and tubes, or have their right to a free travel pass taken away. A "three-point pledge" orders these marauding oiks to refrain from using offensive language and be courteous to other passengers and staff.

Spouts Johnson: "When I was a boy, I was taught to stand up for those less able to... youngsters enjoy the privilege of free travel, but they have to understand that..." and if you remember anything from school, you'll know what comes next, "...with privilege comes responsibility."

Even discounting Boris's own occasional lapses in personal responsibility, one still is stuck with the feeling that this simplistic ruse – aimed at the disgruntled grey vote – is among the most unenforceable ever conceived. For though it's easy to blame teenagers as being the worst and most loutish of passengers, the rudest travelling-public in London are adults. They have jobs, mortgages, iPads, families, a smartly tailored jacket – and no consideration for those less able than themselves.

You don't have to be elderly, disabled or, like me, waddling through the latter stages of pregnancy, to witness how selfish one's fellow commuter can be, but it does tend to be more provocative when you're left hanging from an overhead handlebar with 10 kilos of extra weight suspended from your mid-section.

The Tube, in particular, is such an unpleasant environment for the physically diminished that in fact you'll see very few elderly and disabled using it. Pregnant commuters however are commonplace. London Underground knows that few people give up the "priority seat" without heavy prompting, which is why it dishes out those jaunty "Baby On Board" badges (I'd rather have one that reads, "No, I'm not just fat – unlike you. Now get up!").

Whether it's by wearing humiliating badges or bump-enhancing tops, the impetus is on the pregnant woman to announce her situation – and it rarely works without some additional verbal encouragement. The phrase I use now is, "Would you perhaps mind offering me your seat?" Otherwise, in my experience, the normal scenario is that the seated passengers will stonily ignore you. Rarely, and only after five minutes or so have elapsed, somebody will make the gallant gesture; it will almost always be a woman.

I'm afraid to say that the worst offenders are always well-off middle-aged men, (Boris's own demographic, as it happens), who sit in the priority seat with legs splayed, frankly assessing me and then glancing away, as if to say: "It's your own choice to get knocked up. Why should I move?" I know that men say they're afraid of insulting a woman by assuming she's pregnant when she isn't, and I had sympathy for this excuse – until male co-travellers continued to ignore me even as my belly inflated to basketball proportions.

If adult Londoners act like this, it's laughable to imagine that schoolchildren – who at least have the excuse of inexperience – will behave differently, and that extends to the way passengers quite routinely speak to LU staff (raging, eyes popping) and use "offensive language" (freely, particularly on match day).

Boris blames the young for all our discourtesy, because they have no vote in the upcoming mayoral elections in May. Proposing a house "courtesy rule" for kids – which even he admits is "self-enforcing" – is piffle, as he might say, when everywhere teenagers look, their elders behave so thoughtlessly.

Grow the beard, do the PR

James Cameron should be congratulated for his daring solo descent to the deepest point in any of the oceans, the Mariana Trench. Few film-makers have travelled so far in the name of PR – for his expedition is artfully timed with the re-release of Titanic in 3D.

Other directors can learn from Cameron's marvellous stunt. Did Quentin Tarantino never consider slicing off his own right arm with a samurai sword in the name of promotion? Martin Scorsese, taking on all comers in a Las Vegas boxing ring? And what made Stanley Kubrick decide against spending a year on the international space station?

Woody Allen, breaking the record for the world's longest psychotherapy session? George Lucas fronting a sponsored beard-growing competition, finishing with a face as hairy as Chewbacca's – hardly a stretch for the hirsute auteur? Depth of commitment, that's what they lacked.

s.rushton@independent.co.uk