Giddy-uppity

Term used to describe the appearance of uppity male urbanites who have no association with cattle ranching, horses, or agriculture, but choose to wear western attire to create the impression of being a cowboy. Typical Giddy-uppity wear includes overpriced cowboy hats, boots, bolo ties and large shiny belt buckles warn with tight-fitting designer jeans and collared shirts. In addition to cowboy-style clothing, those classified as giddy-uppity are often seen driving sports cars, Cadillacs, and SUVs and can be easily identified by their arrogance and well-groomed facial hair.

Also see poser.

Examples:
"Take off that cowboy hat if you're going to wear a shirt and tie. It makes you look too giddy-uppity".

or

"Check out the giddy-uppity cowboy driving the Porche."