If I'm going to be flying for 20 or more hours, I dress comfortably. Sneakers or sandals, shorts, 2 tee shirts and fresh underwear and a muscle shirt to sleep in. If you care what people think of you as you sit for 10s of hours, you are worrying about the wrong thing.

On the flip side, I shower in the lounge, bring deodorant, and eat foods that won't make me gassy. I say please and thank you to the FAs (which happens hundreds of times a flight on SQ) and if there are any children around I'll play cards or iPad board games with them, pending parental approval.

After a few hours, humor, personality, a good attitude and a smile count more than how you are dressed. And that strikes me as better etiquette than anything forced.