Make it till you fake it.
Most people can’t reliably tell the difference between a fake and real smile. There are consciously moved smile muscles, and unconscious ones. If you don’t know what they are take this BBC smile test first and then again after you read the ditty on muscles. You’ll accomplish two things: better jokes, and a higher appreciation for dental care.
Oh, and with your new found knowledge you can let me know if I’m a faker or not.