The old saying, "Don't look down your nose....", like many Body Language related sounding phrases, has very accurate roots in the real world of human behavior and psychology. This is Australian Prime Minister, Julia Gillard. At the moment of this image, she's exemplifying this pose beautifully. If she were sitting next to me as I write this, I have absolutely no doubt that it was not her intention to appear arrogant or condescending - but these are the messages she is sending. It is another signal for contempt - which very often is overlooked. It is often quite evanescent.
The head is characteristically tilted backwards with simultaneous jutting of the jaw. Although it's not present here, this head tilt, nose up, chin out pose is often accompanied by nostril flaring. Ms. Gillard also shows us the often coexisting lower lip extended in a pseudo-pout pose.
We all occasionally adopt this body language facial expression, because at some moments we truly feel superior. And while the majority of the time, arrogance may not be indicative of someone's over-all personality, for an instant or two these signals will betray their emotional tone. Very often their words will not match this tell. So be wary when you see it, because the nonverbal signals are always correct.