Tuck it in

There's this consensus that tucked-in shirts on girls look ugly, nerdy, and wrong. Almost no young women wear their shirts tucked in unless they have to as part of the dress code for their jobs. For as long as I can remember (since the mid-eighties), tucked-in shirts have been extremely uncool as part of casual wear. Why is this?

I think it's because it's so hard to make a tucked-in shirt look flattering on a woman's body. First of all, it draws attention to the waist, which can be bad if the waist is too wide, too high, or too low. It also makes the hips look wider by making the waist look smaller. And tucking in can make you look heavier than you are: if you're overweight, it draws attention to your tummy, and if you're thin, the blousing effect can hide your flat stomach. I'm guessing that untucked shirts became mainstream because women realized that it was easier to look good in them. The women who contined to tuck in their tops were either very conservative dressers or not very fashion-conscious ones. Tucking in became associated with conformity and nerdiness, and therefore came to be considered not only unflattering, but uncool as well.
Of course, the uncoolness of tucking in makes it ripe for coolness. Now that 70s and 80s styles are so mainstream, I think authentic 70s and 80s styling should come back, too. Plus, as I discovered just now while looking for images of nerdy tucked-in shirts, even L.L.Bean now shows its shirts worn untucked on models on its website. If L.L.Bean has decided tucking in is too uncool for its customers, then it is definitely time for it to become cool for trendy people. (L.L.Bean is a great barometer; they also started producing bootcut pants just as those were about to become unfashionable.)

It's all in the execution, of course. For knit tops, I think it's best to go small and simple: a form-fitting (but not skintight) T-shirt or tank tucked into jeans (the high-waisted ones are perfect). For blouses, form-fitting is a bad idea; tops with very shaped waists that slip perfectly into pants or skirts will give the bad, conservative look. It's better to choose a looser-fitting top, accept that the blousing is going to happen, and embrace it.