In F and J: No flipflops, no sleeveless shirts, no shorts! Unless you're suddenly upgraded without you requesting the upgrade, you must wear at least casual-formal, which means a decent shirt (can be a t-shirt as long as it doesn't have too weird of a motive), proper pants (can be jeans too, but not those with the holes in the legs that are trending right now), socks and normal shoes (though I'd accept decent sneakers as well). As for the ladies, no miniskirts, no hotpants, no tank tops.
In coach: No real dress code, but plelase try not to wear holiday clothing until you're actually in your destination. Which means for both male and female: No flipflops, no tank tops, for males no sandals, no shorts and please always wear socks.
I'm fairly liberal, but there are still limits for me.
Why should passengers flying F and J (Just say First and Business) have to follow a dress code, when those at the back of the planes are exempted? if anything, it should be the other way around, since those flying coach are squeezed together like sardines, and thus the risk of having a pair of pale naked legs hugging your pants is greatly increased.
Last time I flew up front (QR 787, absolutely terrific) I spent 98,7% of the time eating, drinking, looking out of the window, sleeping, reading, and watching TV. The last 1,3% were spent going to the lavatory. There could have been an entire family of Polar Bears in the cabin, and I wouldn't have noticed in the first place. Hell, I was wearing trekking pants, trekking boots, and an army shirt, and the lovely FA still pampered me and gave me top notch service. If I wouldn't notice Polar Bears in the cabin, then I'm sure you wouldn't notice someone wearing flip flops either
I'm gonna wear a pair of shorts and flip flops next time I'm flying Business Class.
Look, even the Captain and First Officer, wore shorts that day. Do you really think it would have been reasonable, to expect me and the crew to wear long pants in 37*C?