Why does my mouth shake when I smile?!

If you're not used to exercising a muscle it will shake when you tense it. Make a fist and tense the muscles in your forearm, if you're not used to lifting weights under tension it's likely your arm will shake - facial muscles are exactly the same. While some Aspies smile a lot, many of us don't. Your facial muscles may get a small workout while you're talking but this doesn't run them through their full range. Try practising smiling several times a day, exaggerating your expressions to fully contract the muscles (you don't have to make it hurt). After a short period of time these underused muscles will become accustomed to working under tension and won't shake any more. Don't worry, it's not a physical manifestation of Asperger's, just that these muscles are underused.

36 year-old Asperger

because you have aspergers syndrome