PRESIDENT Obama

I need a history lesson.  Have we always spoken of the president as if he was our college drinking buddy?  Why do we call him "Obama" instead of President Obama?  Or Barack Obama?  To me, it seems incredibly disrespectful that the man in the highest elected office is spoken of in such a familiar manner.  And this has nothing do to with being a Democrat or a Republican.  It is about respecting the leader of your nation.