I didn't even like running in boxer shorts and baggy OD fatigue pants when I first joined the US Army (white boxers were our sole issue, and before the camo BDU we had solid olive drab). A lot of us bought and wore our own tighty-whites for greater comfort during running & marching. Here's a story that explains the reason further:
In 1969 I saw my Army Recruiter for the last time in his office, my next stop the processing station before leaving for Basic Training. And he went to a supply cabinet and got a dark blue plastic cinch bag with a tie cord, big enough to hold a couple of grapefruit.
"This is a complimentary comfort kit the Salvation Army provides to new recruits," he explained. And sure enough on its side was printed the Salvation Army logo & name in bright red.
I was kinda taken aback; I thought I was joining the ranks of the US Army, not the ranks of the destitute. And he started pulling things out of it to show me, mostly toiletries, until he got to a plastic powder container.
"Now put lots of this powder in your boots," he told me, "to prevent blisters, and buy more when it's gone. And put it all over your balls, too, or else you'll get a bad rash from marching and running, cause they're gonna sweat a lot and rub against your legs."
OK, this Sergeant is telling me what to do with my balls in a matter-of-fact manner. And he's telling me they're gonna suffer from rash, from my high activity level and profuse sweating. So I'm sitting there thinking to myself: "What the HELL have I just gotten myself into?" LOL!
BTW, I never did get blisters from my boots. Nor a jock rash, because like the other recruits I bought Jockey shorts at the PX as soon as we were allowed to go there. (For background, in the Reception Station we were stripped naked of all our civilian clothes we wore, that were put into shipping boxes and sent back home at government expense, or wherever we came from. Hence we only had what we were officially issued to wear, that included those white cotton boxer shorts)