A few people posted about button down (button up...) shirts and I thought I'd wear one today. This is a men's flannel shirt from Uniqlo, XS. It may not be to everyone's taste but I love the fit, though I have to roll the sleeves. It has room for my wide shoulders. My arms can move freely. And it doesn't puff out in front as much as the women's "boyfriend" shirts I own. So I guess the best way for me to get the stolen-from-the-boys effect is to do that, literally. (The shirt also fits my guy perfectly.)
By the way, for the fastidious wordsmiths, this one is literally a button down (the collar buttons) but regardless, I decided ages ago that I like the common usage of "button down" to mean a shirt with buttons.
I only wish my arms were longer so I could wear men's shirts with sleeves unrolled!