George Clooney is, in most people's opinion, a pretty good actor - and this is obviously a posed photograph. But what's not so obvious, is whether he was aware of his exact facial expression at the moment this image was taken. His smile is asymmetrical - both in the eyes and in the mouth. One should always be suspicious of any facial expression where it is more pronounced on one side. It is a solid signal of insincerity. While it certainly doesn't mean the person's entire character is necessarily insincere - it does mean in that moment they were having to "force" facial expressions that weren't congruent with their emotions.