A dear friend, who occasionally weighs in here and on FB, responded to yesterday's Scatter post with this: "Sometimes I don't "get" fashion, i.e., at what point does clothing become costume; hence, transform its wearer into a theatrical "object" to be viewed and entertained by (or not) and why would the person wearing such clothing wish to become merely the vehicle by which it is displayed, said clothing having completely trumped whatever interest might lie within its "human mannequin?'"
Its a really engrossing question. At what point does clothing cease to speak as a part of the Attire dialog and become something outside of it? Or, is that actually a moot point? Is it that the expressiveness of apparel can exist of itself, without direct reference to humanity?
Certainly I have seen and spoken about many examples of avant garde clothing that are so outre' that the humans in them are nearly lost for good and all in the desire to express a conception. So perhaps in that instance, the loss of identification with the person in the clothing is in itself a message being delivered. And in the case of the runway model, the subordination of the person to the outfit is deliberate in order to focus entirely on the presented clothing.
In essence, I think the defining factor is the strength of the personality of the person in view. Some people can carry off clothing styles of real complexity or unusual color or silhouette in a way that makes them look, if not entirely normal, than at least, not so theatrical as to be costume.
So, its not really what is worn, but how it is worn. Is the wearer moving with grace and authority? Is their personality on display without them appearing uneasy? If those questions are answered with a yes, then we will probably not perceive what they have on as costume, but apparel, however unlikely their clothing might be.
Is there a hard line that delineates the territory of apparel from that of costume? No, not in the least. You wouldn't want all this stuff to be TOO easy, would you?