I need to fix my face.

I have been told on more than one occasion to "fix my face".  I must have one of those faces that communicates what I'm thinking.  Sometimes when people are speaking either to me or near me, I can't believe that certain things are actually coming out of their mouths.  I'm sure everyone has felt the same way, it's just that they don't actually show it in their expressions.  Maybe that's not so bad.  It certainly does save a lot of time and energy that you don't have to tell people that what they are saying is simply ridiculous.