I don’t think ‘classy’ means having to forego enjoyment and not having a jolly good time!
I think classy in this context means ‘unpretentious’.
Personally, I would avoid the word "classy" because of the baggage that comes with the root word "class".
However I would identify the following as desirable when flying:
(1) Presentation. Flying is going out in public. It's like dining in a restaurant. One should be dressed and groomed accordingly.
(2) This is adaptable to class of travel & is easier in premium cabins: in F/J, I always change into PJs and ask for my clothes to be stored while I sleep.
(3) If I don't expect to be given PJs (in Y, PE or even many J cabins) I bring my own from a previous flight. I find EY F PJs are the most comfortable.
(4) I also pack spare clothes in case of emergencies and two sets of spare underwear and socks.
(5) Personal hygiene: sadly only EY & EK A380s have showers, but on other aircraft I give myself a sponge bath when I change back from PJs into clothes.
(6) Paper towels aren't great for this purpose: if there are no cloth towels in the toilets, I ask the FAs for some of the refresher towels.
(7) Pay attention to how you smell. I always pack deodorant and perfume in my carry-on bags, and use both liberally.
(8) Stay calm: our emotions impact others, especially when we are confined with strangers for a long flight.
(9) Moderation is preferable to desperation. You don't have to drink
all the champagne. If you do you'll probably just pass out and miss the experience.
(10) Any suggestion that I did this in seat 1A in the F cabin on a CX B773 flying HKG-CDG on Saturday 30 June 2019 is just a malicious rumour.
(11) I am, however, happy to show off the mother of pearl caviar spoon I took from a flight on Saturday 30 June ... oh wait.
(12) Read the room. Some people like to converse with strangers, others prefer to keep their own counsel. And we all have our moments.
(13) If I'm wearing headphones and sunglasses, I'm having a moment. Speak to me at your peril.
(14) Ask for what you want: respectfully. Demanding or rude PAX are no easier or more pleasant to deal with in F than they are in J.
(15) Cultivate a friendly relationship with the FAs. Show some interest and compassion. It's only fair, and as a bonus they will look after you better.
(16) Revisit (8): it really is the most important thing of all.
(17) I was wrong at (16): the most important thing is to remember that flying is a great privilege, and we should savour every moment with joy.
Happy to read feedback and comments but not arguments: this is my personal list, I am sure you all have your own.
Edit: (18) If you have children, take responsibility for them. Talk to them, entertain them, control them. You brought them onboard.