Sometime in the past couple of years, I started wearing my shirts untucked more often than tucked into my pants. Sure, at the wedding I attended on Friday, I tucked in my shirt, as I do whenever I don a tie, but in most other circumstances, whether my shirt is a T, polo, or collared long-sleeved number, it hides my belt buckle.
You could attribute that to a growing belly, but my weight and midriff haven't changed significantly in at least seven years, since I began regular formal weigh-ins at the diabetes clinic I attend. Somehow, looking around, I figured out that most guys aren't tucking in their shirts anymore, and I followed suit. The fashion trend means that, as the New York Times puts it:
Men wearing khakis or suits or jeans and with their broadcloth shirts tucked in look boring or worse [...] They look like the late Tony Randall, natty but distinctly of another time. [...] They look as if their parents had laid out their clothes. And in a sense, they have. On the road to adulthood, there are many concessions to the loss of boyhood's joyous dishevelment. Tucking in shirttails is an early and crucial one.
I do think that untucking a traditional long-tailed dress shirt is a bit gauche, but most modern styles have either shorter shirttails or a flat bottom designed to hang out, so it's not much of a problem. Oddly, the place I'm most likely to tuck in my shirt is when I'm playing in my rock-n-roll band (also the main motivation for my buying a new suit recently), which says something in itself.