Many of us have seen - or been - that able-bodied commuter luxuriating in the rarity of a rush-hour seat, only to jump up guiltily at the sight of a woman standing with a bump or a "Baby on Board" badge.
Well, that's the idea.
For a heavily pregnant London commuter this week, her experience of travelling to work in the capital was starkly different.
The Southern Rail passenger, who is eight months pregnant, has told of how she was forced to stand for two hours on her train journey to work because no-one gave up their seat.
Asking to be named only as Lauren, the 31-year-old marketeer, told the Evening Standard how no one was willing to let her sit down on packed services from Crawley to London Bridge.
Strike action by Southern Rail staff has disrupted services into London and the mother-to-be first took a Thameslink train to East Croydon, where she changed for a train to London Bridge. She stood the whole way.
“Eventually I asked the carriage: ‘Would anybody be able to give me their seat?’ but the response was silence,” she says.
“People don’t like to make eye contact,” she explains. “Everyone just looks down.”
It was only when she was six minutes away from her London Bridge stop that a "gent" told her she should take his seat.
“I shouldn’t need a badge,” she adds. “I’m five foot three and I have a massive bump sticking out ... just a bit of consideration would be nice.”
Southern says it runs a priority seat card scheme for passengers less able to stand and provides assurances to commuters that the person has a “genuine need” for the seat. The train provider says the card makes it less “awkward” for the commuter who has to ask.
It's not the first time a pregnant women has fallen victim to the capital's merciless rush hour and its affect on passengers, a condition we've identified as LLLD (low-level London dickheadedness).
In November, a tube passenger gave up their seat to pregnant Raayan Zafar, who was wearing a Baby on Board badge, only for another commuter to demand "proof" that she was pregnant.
In another slap in the face for pregnant commuters, last summer a clothing firm, Wayward studio, created a mock-up badge that replaces the "Baby on Board" message with the words "I'm important."
A student who wore a fake pregnancy belly to take the undercover "Bump Test" on the London Underground in 2014 found that only 20 out of the 100 passengers who saw her heavily pregnant stomach gave up their seat.
The comments underneath her article on the study shed light on the attitudes of some of those who refuse to move to accommodate pregnant fellow passengers.
They range from acknowledgement they should move - but don't - to vigorous insistence that carrying a child does not make a commuter any less able.
One person even defends their stance by comparing pregnancy to a man carrying heavy golf clubs:
"They’re pregnant, not disabled or unwell. They chose to get into that state and some of the people not giving up a seat may have physical issues of their own."
"If they are fit enough to go to work then they are fit enough to be standing up on the tube - have no problem giving up my seat to somebody less able to stand but a pregnant woman is just a pregnant woman not sick, ill or unable to stand."
"I know it’s out of order but I pretend I don’t see them. I’ve been working hard all day - If I get a seat it’s a luxury - I paid a lot of money for it. Sorry. [:)]"
"I once saw a man carrying a golf case, there were at least 20 clubs there, I’m sure 20 metal sticks weigh more than a fetus, and no one offered him nothing."
"I’ll always stand for someone who is less able than me; not just because she has a ‘baby on board’ badge though!"
Lauren's story has provoked a strong reaction from stylist.co.uk readers, prompting many of your own extraordinary experiences of what it's really like being pregnant on public transport.
What do you think?