I hope this is not too analytical an approach, but is it worth pausing to ponder what we mean when we say that something is or isn't art?
The statement may mean "I do not like this particular work of art". That's fine, but saying it may make your case clearer. It may mean "This particular object does not meet my criteria for qualifying something as a work of art". Again, fine, but again, if you say so, the discussion will focus on your criteria, which will presumably yield a more interesting discussion than "This is art" - "Yes, it is" - "No, it isn't".
Things get more complicated when it's not only about evaluating a particular work of art (or a particular object, if you will), but when you start attaching some social consequence or other to your definition of art. If you say "This painting isn't art, and therefore, I will not visit the musueum where it is displayed", you are of course free to do that, and since the consequences (almost) only relate to you, my only comments are those I made above. But if you say "Since this isn't art, people shouldn't be allowed to see this or the artist should be prohibited from producing further such works", the relevance of your concepts extends beyond yourself and must therefore be weighed more carefully. I am in no way saying that any of the posters of this thread has advocated any such thing. I would only contend that the more far-reaching the consequences are that you attach to your definition, the broader your concept of art has to be. If for no other reason, then to prevent that the concept be turned against you and the art that you are making.
I, me, personally, prefer a definition or concept of art that does not focus on the product, but on the process. To me, art is essentially something you are doing, the process of expressing what you think, see or feel about yourself, your life, the world, whatever. Whether or not your specific ways of expressing yourself, your works of art, are appreciated, understood, cherished, bought by others, is of course interesting and maybe important, but, to my mind, not instrumental for describing something as a work of art. The "problem" with this approach is that to know whether something is a work of art, you would need to sit in the artist's head. Since you can't, you can never be sure that you're not being put on. But I can live with that risk .
Incidentally, this "procedural" concept of art can be a way of appreciating or respecting works of art that you do not like or understand: by appreciating or respecting the process behind it that will be very similar to the process behind your own works, however much your works differ from that other person's.
Sorry for this long post. Thanks for reading.