I'm going to touch upon a touchy subject, but too bad. Appearance is everything in business. If employees (flight attendants or whoever) want to be taken seriously, then they've got to dress the part.
This means clean, ironed uniforms. Straight ties. Correctly fitting dresses and suits. Properly hemmed pants.
Personally, I dress like a friggin slob---but only on days off.
If I go to a Purser meeting and the invitation says, "Business Casual" you can bet I'm still going to wear a tie. In fact, I would never go to any UAL event or activity without wearing a tie and sport jacket at the very least. I don't care how 'causal' their current dress code is.
You ever watch Animal Planet or some other nature show? Look at how the animals interact with each other: They show off teeth, fangs, wings, chest, beaks, claws, whatever in an attempt to display dominance. Humans do the same with clothes to display authority--and I've seen it happen time and time again on the planes.
There seems to be a trend in large corporations to switch to a 'causal culture'. First, it was 'relaxed Fridays'. Now, UAL and many other companies have what appears to be 'relaxed Everydays.' But folks, make no mistake about it, you would never see the CEO in anything less than a suit. Even on a Friday.
An important thing to remember: The point isn't to be overdressed. Rather, it is to be properly dressed, slightly more professional then the situation calls for. Try it out and see if you don't notice more respectful treatment.