bumpy road boner
When you're driving along a bumpy road, and the constant bumping around makes your body get confused due to all the penis flopage occuring within your pants, and to your surprise you get a boner. Also known as a "brb."
While taking the buggy for a spin I got a bumpy road boner and had to lie about why I didn't want to get up from the drivers seat. "I'm just checking the gauges," I said.