A facial expression used by individuals in response to open expressions of having beef (i.e. somebody snitching on an individual's: gross negligence, underwhelming skill abilities, delusions of grandeur.)
Did you see the look on that driver's face? He did a meanmug and cut me off when I had the right of way. I'm not mad, I'm just disappointed.
noun. one who meanmugs. meanmug means to stare down or 'grill' someone. The etymology is mean+mug (meaning face). as in: to show someone a mean/angry face = to meanmug = to stare.