One of my most liberating moments of epiphany (so far) in development as a feminist was realizing how meaningless clothing sizes are.
They seriously are some of the most meaningless numbers in human history. For the most part once you move past XS, M/L, and XL, all those numbers 00, 2, 4, 8, 10, 28, 14 etc. can almost mean anything. Numeric clothing sizes fluctuate hugely, like roller coasters, by store, designer, country, clothing range, prince range, and age (of target customer). To see if something truly fits, flatters, and/or is comfortable you need to do a cursory and educated guess (do you normally wear M's or L's, then you probably know not to try the 00), and then either get out the old tape measure or you need to try it on.
To brag a little, I think I always knew that clothing sizes were a meaningless measurement. As a teenager I remember fitting into and wearing a lot of different sizes, but being confused and anxious about why I couldn't find the One True Number that I was supposed to fit into. Little did I know that there is no such One True Number.
Also, growing up with two sisters and a large extended family, I was used to wearing 'hand-me-downs' so perhaps on some level I understood that bodies naturally change and fit into different sizes; and also being one for caring about aesthetics more than status symbols, Child Me usually cared more about whether the clothing item was fun, flashy, colorful etc. than the number stamped on a tag on the inside that no one ever saw. But again, as I got older, I noticed a lot more of my friends and peers worrying over their 'dress size' and worried that someone would ask me about mine and I wouldn't be able to provide an accurate or definitive answer.
However, in college, I was reading the AMAZING book, The Body Project, (which all American women should read and) which chronicles the evolution of American girls through diaries and in conjunction with the history of American consumerism and body-related technologies. (Want to know the history of feminine hygiene products? I did. And this book covers it. It's a pretty great book.)