Laura, are you thinking of this post from A Dress a Day? I found it revelatory too & I still repeat the 'prettiness is not rent you pay for occupying a space marked female' bit to myself often.
I spent my adolescence hating my looks; there were days I felt I was so ugly I shouldn't go out and inflict myself on the world. *head shake* I think it started because my mom & sister both have the classic, All American cheerleader type of look, with small, pert little features, while my features are much broader, including my snub nose (the subject of much loathing). And I developed acne as soon as puberty hit. And my thick, light blonde hair suddenly turned darker (to the charmingly named 'dishwater blonde') and started mysteriously falling out, becoming thin over the course of a few months (my mom thought I was going to end up bald). I also look a lot like my dad, and grew up being constantly told by everyone that I was his spitting image; this is not a kind thing to tell an insecure teenager really, as it meant that I felt I had a man's face. And then I was so thin-10 lbs less than I am now-I hadn't developed prominent curves, so I felt like a looked like a prepubescent boy. Ugh. It was a terrible time, and I generally feared that most people who saw me would think I was a man masquerading as a woman. Luckily, early in my college career I decided it was silly to spend that much energy hating things I couldn't change, so I started working on my self esteem; it took 2-3 years but eventually I retrained my default thoughts. Nowadays, if it's not something I'd say about my best friend, I don't think it about myself. Thinking about it, though, I think that fear is why I surprised the more 'romantic' style leanings I had for a long time; I was afraid they'd look ridiculous on my masculine-looking self. Thank goodness I've gotten over that.
Which is not to say I don't still have my insecurities. My struggle with acne persisted until about a year ago, when my dermatologist sister had me try a medicine that's worked wonders. But my adult acne was the type that scarred, so I'm still dealing with those scars (which should fade in 2-3 years) and mild rosacea. Plus, I have quite large pores. My skin is definitely my biggest insecurity! It's actually why I got interested in my most flattering colours, to moderate its flaws. But I try to remind myself that most people who I'm talking with are looking at my eyes, not examining my skin. I admit that's much easier to remember now that I don't get acne regularly though. And there's no 'embrace your skin just the way it is' movement, like the body love movement.
Anyway, I was so surprised to hear about everyone's insecurities, as I've seen you all in outfit photos and never even noticed what you're talking about! We really are our own worst critics. *hugs*