In the above video, one of my favorite actors, Matt Damon gives us several beautiful demonstrations of an "Inward Lip Roll". Here he was attending the recent 2011 "Save Our Schools" March in Washington D.C. The inward lip roll is a sign of increased anxiety and stress - and it very often has a component of anger within it. The lips are, of course, an extremely sensitive tissue. Touching one or both with the hand/fingers, tongue, teeth or other lip is an example of a manipulator/adaptor/pacifier (MAP). We display MAPs during times of increased anxiety. It is helpful to think of the inward lip roll as an attempt to control a negative emotional "soup" - with the main ingredient often being anger.
What other signs of anger are displayed? Anxiety? Contempt (see photo too)? Are there any microexpressions? This is an excellent short video with several outstanding nonverbal examples. Body language is almost impossible to suppress. Our true emotions will always "leak" or "pour" out. Even great actors cannot control their emotions when they are in the thick of them.