The first guy to offer me his seat was quite young. That raised alarm bells. Usually it's older gentlemen who leap to their feet when they see a woman standing (presumably for fear her uterus may be heading southwards in a drippy fashion).
I smiled a no and went back to the Evening Standard. But a couple of minutes later, a young woman sitting just next to me at belly-button level leapt to her feet and gestured maniacally towards her vacant seat.
Even then, I was slow to catch on.
"No... thanks... are you getting off?" I stuttered - and then, as the horrible realisation sank in: "Do you think I'm pregnant?"
"Yes, no worries! Sit down!" she shouted over the tinny thumping of her iPod. I stared at her crazily (it may have been with only one eye) and watched as realisation began to dawn on her.
Seldom have I seen someone become so embarrassed, so fast. The colour in her cheeks rose faster than the sun over African plains at the beginning of The Lion King. She ripped her headphones out and started mouthing wordlessly. Time for me to say something.
"I'm not pregnant, I'm just... a bit... fat?" I faltered, realising as I said it that it was absolutely not the right thing to say. Actual tears leapt into her eyes. She started gabbling: "No! No way! Not pregnant? Not fat! Oh God! You're not fat! I'm so sorry!"
I pressed the woman back into her seat, apologising profusely for embarrassing her, thanking her for her kindness, and congratulating her on her public spiritedness, before breaking eye contact as soon as was logistically possible and returning to the paper.
But the words swam in front of my eyes. In a frenzy of mortification, I cast around the carriage, searching desperately for a trough of Monster Munch into which to sink my face.
Big mistake. The gaze of every single person in the carriage was fixated on my abdomen. As soon as they clocked me looking, they instantly looked away to their own papers, feet, or the buttocks of strangers at eye level.
I clutched the base of the Standard to my stomach and pretended to read (again, probably with just one eye).
How could this be happening? I couldn't possibly be that fat. In fact, I'd lost a lot of weight over the last couple of years and am now a size 14 (the slimmest I've been since I was 14). But that's obviously not good enough if I look pregnant. And not just a bit pregnant - enough to make two sober and presumably rational adults assume that I am pregnant enough to need to sit down on public transport. That's, what, like, seven months?
Oh my god. Oh my god. Oh my GOD.
Maybe I am pregnant. Maybe I am one of those women who gives birth on the toilet having never realised they were up the duff in the first place. Maybe I'm actually nearly full-term, and only modesty and poor self-esteem has kept me from this realisation until now. Yes. Yes!
I try to catch a glimpse of my reflection in the window behind my benefactress's head and instantly regret it.
Huuur (I say, internally). Huuuuuuuurrrrr. There is a definite bulge, which is emphasised by my slouch against the pole. I immediately stand to attention - still the bulge remains.
This is a dress I bought to go on holiday in 2012, when I was a size 16-18. It is from Joules. It is orange, it has an empire line and it is a size too big. The empire line used to hug my ribcage: now it hangs loosely, creating a pouch of material around the mid-region.
Oh Christ. It's just the sodding dress. It's the DRESS. For fuck's sake, I've worked hard and lost all that weight only for my clothing to attack me when I least expect it.
The world is suddenly a brighter place. The woman who offered me her seat has either gotten off or died - I don't know which. I resolve to burn the dress as soon as I get home, change trains at Edgeware Road and start thinking about other situations me and my dress could put ourselves in. Smoking outside a pub whilst necking vodka has a certain appeal.
By the time I disembark at Gloucester Road I am resting my hand contemplatively on my belly.
Kyle. That's a good name for my vodka baby.
Follow Christina Kenny on Twitter: www.twitter.com/dfordalrymple