Susie Rushton: Now I'm pregnant I see how rude people are

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.

Even discounting Boris's own occasional lapses in personal responsibility, one still is stuck with the feeling that this simplistic ruse 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.

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.

I'm afraid to say that the worst offenders are always well-off middle-aged men. 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 will behave differently. Proposing a house "courtesy rule" for kids is piffle, as Boris might say, when everywhere teenagers look, their elders behave so thoughtlessly.