I can fit in sizes 2, 4, 6, and 8, depending on the clothing company, which has made shopping not just confusing but embarrassing.

The last time I went clothes shopping, I got trapped in a dress. I couldn't budge the zipper. I couldn't slide the dress up over my head or down past my hips. After working up a sweat trying to emancipate myself from the boucle sheath, it was clear I wouldn't escape without a) help from strangers and/or b) the Jaws of Life.

Within minutes, I had corralled a fitting-room attendant and three other shoppers to free me from the dress. But I didnt feel red-faced mortification until an unhelpful saleswoman sniffed, "Well, it looks like someone should have tried on a larger size."

OH, NO SHE DIDN'T! (Oh, yes, she did.) When I recounted the story to friends, they all had the same reaction I had. Standing half-naked in front of strangers: No big whoop. A stranger suggesting you're larger than you think you are: Never-leave-the-house-again humiliating.

Though no one I know has ever had a shopping trip turn into a rescue operation, it seems every woman is obsessed with sizes. One mother confessed to cutting the labels out of her postpartum shorts because they were a size higher than what she wore prepregnancy. A friend who works for an upscale clothing company spoke of clients who order whole wardrobes in "their size" without trying them on. "I warn them that fit varies from piece to piece," she says, "but they refuse to listen." Many of these items end up being returned or, worse, hanging in the closet unworn like a museum exhibit titled "The Size I Used to Be … or Never Was."

Have you noticed that there are certain stores in which you're miraculously a size or two smaller than elsewhere? Some friends admitted to buying items that werent that cute simply because the smaller number on the tag was an ego-booster. This downsizing trick seems to be an American phenomenon. My European friend Lene, a former model, tells me that clothing across the Atlantic tends to be more uniform. "American stores seem to think that shoppers need clothes in smaller sizes to feel good about themselves," she says. Fashion-industry insiders actually call this technique "vanity sizing" because it caters to our dysmorphic egos.

Because sizing isnt standardized, Im a size 2, 4, 6, and 8, all at the same time. My true size falls somewhere in the middle, which, technically, makes me a size 5. Until recently this odd-numbered sizing only existed in the juniors department—and no woman over 30 should shop in the juniors department. (I'm looking at you, Dina Lohan.) Our obsession with numbers must have inspired at least one plus-size retailer to create a new sizing system wherein my XXL mother-in-law is also a size 5. This was amusing at first ("Ha! Were the same size!"), but it was ultimately rejected by my mother-in-law for being an "obvious marketing ploy." Shouldn't we all be savvy enough to buy clothes that actually look and feel good, regardless of the number on the tag?

Which brings me back to my fitting-room debacle. The irony of that snippy saleswomans accusation? The dress was actually a larger size than I usually buy. If I was lured by any tag, it was the one that read CLEARANCE. Size wasnt the problem, the cheap zipper was. THE ZIPPER, I TELL YOU.

Megan McCafferty is the author of Fourth Comings.