Originally part of the term "road hard and put up wet" in reference to horses. As in the horse was put through a hard workout and then wasn't brushed down and cared for afterwards, which can make a horse sick enough to die. Now used to refer to someone who looks unkempt, strung out, tired, dirty, etc.

When you eat dirt for the first time and leave your family to build a shack in the woods

road hard is a term that describes the way a particular thing looks, usually a girl, when it or she looks rather gnarley, respectively.

this is when you are riding on a bumpy road and guys get a boner.