I've actually thought about this matter some time ago, and came to the conclusion that you can come up with something as long as you define it well enough. For example, a poster a few posts above this one says "the sky is blue" - I could argue that by stating that I'm Dutch and I don't do "blue", only "blauw". Or by stating that I called what you guys call "blue", "pinkapoppel".
If you change the original point however, to "The majority of the English speaking beings on this planet will answer "blue" to the question "which colour is the sky?"" it becomes a lot harder to find a loophole. One could probably find one for that sentence, but then again I haven't gone as far as to completely defining every word I use in my original statement in utmost detail.
Then again, ironically enough, your definition of 'argue' plays a role here as well. Random internet dictionary [http://esl.about.com/od/intermediatevocabulary/p/word323.htm] defines argue as "to offer reasons for or against something", which would remove a damn load of options - saying "I disagree" or "It can't be proven" isn't "offering reasons for or against something". If you go with the site's other definition of "to dispute; to disagree", however, literally ANYTHING can be argued against. Whatever you state, I can disagree with it, how stupid that might be.