In Pixar's movie, Cars, what is Wingo lauging at as he looks at his reflection?

In the scene where Mack is nodding off and the three imports pull up along side of him, Wingo slows down to look at something on the side of Mack's trailer - or his own reflection, turns on a light to illuminate the truck, then laughs to himself. I have paused the movie so many times and I can't figure out what he's laughing about.