Devil's advocate.
In my opinion, the jumpseat policies should be enforced with a talk or denial. Getting denied will be a lesson not soon forgotten. And just maybe, you’ll keep whoever from making a fool of themselves later.
A frequent defense of enforcement is "to educate them for the future." This common refrain of "educating" and "mentoring" is a little condescending, but beyond that this defense's sole purpose is to perpetuate a policy that in this day and age could actually use revising. Why keep putting energy into it? Sort of a sunk cost fallacy.
Professionalism, is important to all of our job securities. The way you dress is part of that.
The Air Canada Captain I saw the other day with a beard looked very professional. Surely most of us are on board with revising beard policy assuming it doesn't cost anything? But to be real, how many passengers really care that a person in jeans went into the flight deck? How many would even notice? Realistically, it has no bearing on anything.
A lot of people before you have done a lot more for a lot less and for a much longer time.
And my grandfather fought in WWII, but that doesn't have much relevance here. I understand if company policy is XYZ, we have to do XYZ, but that doesn't necessitate over-the-top enforcement. And in the meantime, it's okay to nudge our organizations towards contemporary viewpoints on professionalism. This job doesn't have to be hard.