Genuinely one of my favorite details in MASH is how every character manages to display their unique identity through clothes, despite the uniform. They've all got a couple personal garments of civilian clothing mixed in with their preferred ways of modifying their fatigues, and that's so cool.
Hawkeye wears his undershirt untucked and his overshirt unbuttoned, plus he removed his epaulettes (Trapper is more or less the same). Radar has his overshirt unbuttoned but still tucks in his undershirt, and he wears that iconic hat that's definitely not standard regulation. Henry has his fishing gear or college sweater, and only pulls out the proper uniform shirt and hat if big brass are coming to camp. Frank and Charles both button and tuck in their shirts, but Frank usually wears his hat while Charles does not. Potter buttons his shirt, but never tucks it in. Margaret starts out dressing pretty uniform standard, but by the later seasons she usually replaces her shirt with a sweater or sweatshirt of some kind. Klinger, of course, has a variety of iconic fits.
BJ is definitely the most dramatic example, and it feels very intentional that by the later seasons the only part of his uniform he wears are the pants. He's got his iconic pink henley, plus an army shirt he made into a vest or a pair of red suspenders. He never even wears combat boots, it's converse all the way for him! To top it all off, he's got overlong hair and a goofy mustache; that man is showing disrespect for army regulations in every aspect of his physical appearance. It's very similar to Klinger, in my opinion; except BJ skipped right past the veneer of trying to prove he's crazy to "this is what I want to wear and I won't let this fuckass institution police how I'll present myself"
There's just so much character in how all of them choose to express themselves, despite living in a situation intent on stripping them of their individual humanity! I could do individual character analysis for all of their outfits, even though they're supposedly wearing the same thing.
Insane Trapper Girl correction on this- Trapper almost always tucks his shirt in and wears a belt. When they're relaxing, Hawkeye keeps his shirt on but Trapper takes his off. They have very similar civvies of sweaters/robes/Hawaiian shirts, but Hawkeye's are usually oversized and Trapper's are fitted. This is part of why there's a perception in fanon of a size difference when they're objectively almost identical in proportion and switch costumes occasionally. In extrapolating what these differences in wardrobe mean for the characters, I like to headcanon Trapper cares more about appearances, and is a little fashion conscious/vain, and tries to style his uniform in a way that Looks Good but also doesn't look like he gives a fuck about rank or military bearing.
