As ice-breakers go, it's a high risk one: "Congratulations! When are you due?"
Especially if it turns out the person you're talking to isn't pregnant after all.
Yesterday, it was my turn to be on the receiving end.
I was wearing a high-waisted, pleated skirt that, yes, was feeling a little snug around the waist, post-chocolate brownie. But I'm a size 10 (even a triumphant 8 in generous fashion chainstores). I may not have a washboard stomach and am roughly the same size as Kate Middleton at 4 months along - but I'm generally pretty happy with how everything hangs together.
Or so I thought.
"Oh God, I'm so sorry," said the beauty therapist who'd just put her perfectly pedicured foot in it. "You don't even look pregnant. You've got a tiny waist.
Really. Ignore me. It's just that a client was really offended earlier today when I didn't realise she was pregnant, so I thought I'd best check."
Right. (Hint: asking all female customers whether they're expecting is a poor business plan.)
I was mortified. After all, I'd basically just been called fat to my face. Later that evening, I stood in front of the mirror and examined my phantom bump. Did my stomach really bulge that much? Enough for someone to think I looked pregnant? Surely no one actually asks whether you're expecting unless they're really sure you are? That means I don't just look pregnant. I must look elasticated-waistband wearing, nipple pump-ready, call-the-midwife pregnant. Oh God.
And I'm not alone. The internet is awash with comments from people who have suffered the same indignity. From the bride whose father-in-law grabbed a champagne glass from her hand and lectured the wedding party on the dangers of drinking during pregnancy to the shop worker who was asked, "So what's in there?" Not to mention the recently married woman who was subjected to a relative stroking her belly and cooing, before asking when she was due.
One writer contacted me on Twitter, once I had shared my own experience, to say, "Ran before work and was yet to eat. Felt dizzy, leaned on a wall, when a guy came over and said, 'that's what happens when you exercise while pregnant'.
Needless to say, the perpetrator is usually equally horrified. My mum confessed to having committed the faux pas in the local pharmacy, muttering an excuse about the woman's dress being "very flowing" and backing shame-faced out of the door ("I started using a different chemist after that," she said). Another friend admitted to questioning a colleague who then turned around and screamed to the whole office: "Why does everyone keep asking whether I'm pregnant?!"
Indeed, there doesn't seem to be a general consensus on how to react. The women I asked were broadly split between the "no, I'm just fat thanks" camp and those who bite their bottom lip until enough distance has been achieved for the tears to roll.
So what's going on? When did it become acceptable to seize on the slightest perceived flaw or change in someone else's figure - especially when that person is practically a stranger?
Just because we're free - nay, encouraged - to examine and comment on a celebrity's every curve on gossip websites, it doesn't give us the right to do it to each in other in real life. This isn't an open invitation to prod, poke and potentially humiliate each other.
It also shows how out of proportion our impression of the female form is.
Just to be clear: the concave stomachs of Cara Delevigne and Rihanna are not the norm.
The rounded tummies of we sometimes gluttonous folk, who drink beer and always order a side of chips, are.
Must we resort to wearing Bridget Jones' "scary stomach-holding-in pants" all the time - just to avoid being interrogated about our due dates?
So, a lesson in female etiquette: don't ask a woman whether she's pregnant unless you can see a head emerging.
Oh, and Kate, if you want rid of your maternity wardrobe, you know where to find me.