My wife has a theory about really loud, really jacked up pickup trucks: she calls them DRTs.
The theory was reinforced tonight as we were passed by a pickup with odd shaped things hanging down from the back bumper. We got closer, got a good look, and it became weirdly clear what they were. It looked like this.
I got home, searched for "trailer hitch testicles" (because that is what they looked like), and found them: Bumper Nuts. Available in a variety of colors and brass.