I avoid shorts on planes. Otherwise I've traveled in anything from a suit & tie to jeans and sneakers, regardless of class of service. And if the only thing I'm doing that is traveling, I often don't shave.

And I second the taking off of shoes -- I avoid it like the plague. The only times I've done it is on the overnight int'l flights where I put the extra socks from those amentiy kits on over my own socks. I especially don't understand people who do it before takeoff. Those shoes could become dangerous in case of an emergency....