"George W. Bush: All Hat, No Cattle"

I have no idea what this means. It was on a sticker in the back of a Dodge Ram. Are we to infer that "cattle" is synonymous with "brains"? "Balls"? Then what does the hat replace? Is it like saying he's a cowboy with no herd? Or maybe a shepard with no flock? Seems he'd appreciate THAT analogy a bit more...
The fact that it was in the back of a Dodge Ram with Massachusetts plates and what appeared to be LITERAL brass balls hanging off the bumper further confuses me. I had no idea there were rednecks in Mass., and that they were voting Democrat. Unless I read into that sticker wrong. Hats are, after all, important to rednecks. So are cattle. See my dilemma? And I had an hour on the turnpike alone to contemplate this.
Discuss, then pass your answers to the front.