As typical you are assuming more than what is stated. In the case of a mug flying across the room you could prove supernatural if all other reasonable natural causes were ruled out, hence the definition of the word. But again, this isn't enough for you.
Like I said, there could be
millions of "possible" explanations for a cup flying across a room. Trying to "rule out" every single one of them would be a complete waste of time, and nearly impossible. This is why deductive reasoning is not commonly used in science - because the amount of "possible" explanations for any known phenomena are almost incalculable.
Also, you're putting words in my mouth.
My grasp of science is quite firm, but I'm open to possibilities that science can't completely rule out. Take aliens, extraterrestrial life forms, for instance. Today probability makes the assumption that life must exist somewhere in the universe besides earth, but it's still a debated subject. Now take that 100 years ago and what kind of reception would that garner?
And where's the comparison between aliens and the supernatural? Science also can't "completely rule out" fairies, elves, Hogwarts or the Flying Spaghetti Monster. If told you I saw a mug fly across the room and it was proof of fairies, would you be "open minded" to that assertion as well?
Being open to possibilities is fine. The problem is that you're not just open to them, you've repeatedly asserted that the supernatural exists - and that the only reason we don't accept it is because our standards of evidence are too high. This is where you cross the line from just spouting hypothetically to actually needing evidence of your claims. If all you can do is say "well, we might find evidence in the future - be open minded!" then your case is hardly strong.