My psychologist described my facial expressions as thus: mostly flat unless talking, where I will show appropriate expressions. She described it as akin to watching an on/off switch in action. She went on to say that it used to perturb her a little when she was talking to me during our initial sessions, but she got used to it and now is okay with it.
A former supervisor of mine also mentioned that I had a rather "flat" expression, but she also grew accustomed to it once she worked out that me looking at her flatly didn't mean I wasn't listening to her, because after she finished talking she noticed I would carry out her instructions.
I thought those comments were interesting to me because I'm not vain enough to constantly hold a mirror to my face to check my facial expressions 
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Said the apple to the orange,
"Oh, I wanted you to come
Close to me and
Kiss me to the core."
Think you're ASD? Get thee to a professional!