This kid suffers from a serious case of PCS (Photographers Child Syndrome) and when a camera is pointed in his direction he usually flashes a overly huge fake smile. I have tried many things to get him to make a more natural smile. The thing I have found that works best is to talk about that thing that is endlessly and universally hysterical to 5 year olds everywhere...poop. Another thing that works is when I show him a picture I just took of his weird fake smile.
Here's a real smile...induced by a little potty humor.