A "dirtbag" in climbing/skiing circles is someone who lives in a beat up van, has very little money and spends all their time and (meager) money driving for spot to spot, devoting their entire life to climbing/skiing.

There are dirtbag surfers as well. They only get so dirty because they're always in the ocean.

Ah thanks. No “scumbag” implications? Because not traveling in outdoor circles I think of “dirtbag” as a guy who sleeps with teenage girls and sells stolen property out of a van.