Especially on long flights, I dress for comfort. I am purely a leisure traveller and spent years as a cheap backpacker. I usually wear long stretchy pants and a t-shirt so if I am lucky and the flight is empty enough I can sleep across a middle row without exposing anything. I never notice what other people wear and could care less. I often wondered why people feel the need to wear business attire on planes-isn't it bad enough you have to wear those get-ups for the office? I am fortunate enough to be in a profession (accounts clerk) where I don't have to dress up-just vaguely smart casual.

If I were a FA, I would NOT treat dressed-up people better than others.