The phrase comes from the long-running rivalry between Mack and Peterbilt, two iconic American semi-truck makers whose drivers love to argue over which rig rules the road. The line circulates as a piece of trucker humor, the kind of thing heard on the CB radio or at truck stops. It spread online through trucking meme pages and short-form video, where drivers pair it with clips of polished chrome Peterbilts. Today it survives as a lighthearted badge of brand loyalty among big-rig enthusiasts.