JM and others...I am not sure why, but the "what is art?" question seems to invite an attitude of "anything goes" among otherwise intellectually careful people. I can assure you that this topic has been covered in depth and with care and that the experts seem to agree on at least this...they disagree that "anything can be art". Unless by that you simply mean an artist can appropriate "anything" and use it in an art context, but that is almost never what people mean by such things.
As pointed out above, the term "art" is overloaded and there is an accepted sense which simply implies a high level of skill...e.g. "the art of computer programming". Most people, when they say "anything can be art" mean that anything worth doing can be done well and with skill, and doing so raises the activity to the level of an art.
But that use of the word "art" is so different than art as we mean it in the context of fine art, music, dance, theater, etc. that it is terribly misleading. I wish there was a completely different word for that kind of thing because the confusion is pervasive and generally unrecognized.
That's not to say that skill isn't practiced in some/most art. But such skill isn't a requirement or even the primary point of art as a discipline.
For anyone interested in a serious treatment of the "what is art?" question I'd suggest "Philosophy of Art - a contemporary introduction" by Noel Carroll. It hits all of the traditional theories and most of the primary current directions.
