Trucker's wood

Most truckers actually drive around with an intense, priapic erection in their pants a good portion of their day. This is called trucker's wood and is probably the result of prolonged physical exertion (of operating the truck) vehicle vibrations and possibly an above-normal virility associated with truckers.
Truck operators generally don't speak of this to strangers, but on the road they all know that everyone on that special low-frequency radio is driving around the country with a freakish hard-on.