This is a photo of Christine Lagarde, France's Finance Minister, at a News Conference in November of 2010 in Lyon. There is the classic display of moderate disgust exemplified by a great display of Nostril Flaring with accompanying mid-face tightening. When it comes to disgust (or contempt) what is rarely discussed in body language texts - Ms. Lagarde illustrates rather nicely. She is leaning dramatically away from the object of disgust. We lean, and/or turn away from those we dislike, disrespect or distrust - often suddenly - and all three of these feelings can overlap with disgust. It's amazing how often this tell is glossed over.
Interestingly, Ms. Lagarde was not angry at the moment of this photo. Another emotion we often see with disgust is beautifully illustrated by her elevated medial (inner) eyebrows along with her entire forehead. In this context, these changes illustrate disbelief and they may only be there for a brief flash (as little as 0.04 of a second!). She is disgusted, and her emotional brain can't quite believe what she is seeing and/or hearing.
If you see this expression directed at you - and you know you're telling the truth - you must stop the conversation and address the specifics behind the other's disbelief. You'll have some explaining to do - but you cannot pass up this golden moment to correct a misplaced incredulity - lest it gets a chance to set in and becomes more of a permanent belief. Certainly be tactful and ask open-ended questions - use the Socratic Method (don't ever say "I can read your body language and I know you're don't believe me"). Always remember the potency of your ability to change another's mind drops off dramatically as time passes. Therein lies one of the great values of leaning, practicing and using body language.