Can't pump gas? Because it looks undignified?
I think it is called an unauthorized stop, or something like that when you are commuting to and from work.
I'd do it but I am off to bed now. Try googling military uniform regulations or army uniform regulations dod, etc.
The theory used to be that BDU's and fatigues before them, were WORK uniforms, not spit and polish dress uniforms (and in some cases, as with aircraft or vehicle mechanics could be pretty groady) and did not present the desired "Military Appearance" that the brass were trying for.
Then about 1985 or so, the notion that fatigues, BDUs, flight and tanker suits (green Nomex jumpsuits) as well, were "warrior clothing" and were just the sort of "military image" that needed to be projected.
Personally I've found it kind of weird to have military folks in engineering or programmatic meetings, some fairly formal, wearing BDU's or flight suits.
Used to be you couldn't wear fatigues/BDUs on civilian aircraft too, but today at any major hub, you'll see almost all the military folks in BDUs.