I have been flying for 14 years and am a csd/ifs.
For me its chinos and shirt for shorthaul, tie and jacket aswell for longhaul. I get there early, I'm always ultra polite even when staff are being really grumpy and rude.
I'm always happy just to get on. Upgrades are nice but not expected. I drink water , decline the meal unless I'm starving and try and keep my head down.
My worst nightmare when in charge is the staff family ( normally flightdeck have to say) who manage to get on the flight but are seperated. They get on and and then try and revise the whole seating plan to get themselves together. Then they wonder up to business and see free seats and start demanding an upgrade for themselves and their family who are all dressed in jeans and t shirts..