Giada De Laurentiis is a gorgeous lady and a great chef with an incredibly insincere smile. I wish I could cook like her, and I'd love to have my own television show, but Giada needs a little practice in the smile department. The top half of her face is doing a pretty good job at a "Social Smile" - her eyes are partially closed and her forehead is fairly relaxed.
When you look at Ms. De Laurentiis's mouth though, it is reminiscent of elementary school on picture day - "Say cheese!" When a sincere smile is displayed, the lower teeth are just not visible unless you're looking down from considerable height at the "smiler". Giada's bottom teeth are nearly as visible as her top ones. This is because her mouth is stretched out to the sides (similar to that of a fear display) rather than primarily upwards as they would be in a sincere smile.
If I were coaching this beautiful cook, among other things, I'd tell Giada that the best way to have a sincere appearing smile is to "Lead with your eyes, and your mouth will follow".