TL;DR: Man spends 5 minutes thinking about Bitcoin on a plane and comes to conclusions which may or may not be correct. Shares them with people because he is super duper important.
http://en.wikipedia.org/wiki/Nouriel_Roubini
You can agree or disagree with his argument, but snidely dismissing him as someone without expertise who mistakenly thinks he is "super duper important" is silly.