springheel_jack has produced a handy guide for the perplexed. Useful only if the person you’re talking to is actually perplexed and not a sociopath, but hey, we can’t have everything.
More than 40 years ago, my father wrote a short story called “Dr. Pettigott’s Face.” The eponymous doctor of the story has a theory that pushing the face into happy expressions will make people happy, and has constructed a machine to do this. I remember that for years he had a correspondence with some neuro researcher who was interested in facial expressions because the guy liked the story so much. The title has been a shorthand in our family for people trying to reverse engineer things in weird ways.
The polyvagal theory and some of its implications suggest that there may be a grain of truth in this. The connections between emotion and facial expression are very tight and it’s possible that it “goes both ways”. This story from the LA Times on Sunday is fascinating: