First of all, I would like to set a base definition for the term “dirtbag.” There are a handful of applicable (and entertaining) definitions on Urbandictionary.com, but I refer you to Matt Samet’s definition from the very handy, dandy Climbing Dictionary:
Dirtbag n,v: More romantically, the word connotes a climbing bum, one who proudly eschews the workaday life for his passion. More pejoratively, a dirtbag is a broke, unclean, food-and belay-scrounging lowlife, loath to work for money and happiest bumming rides from crag to crag as part of his possibly larcenous existence.
Climbing bum n: A more loving synonym for dirtbag. Like a ski or surf bum, a climbing bum lives a financially marginal existence, which frees him to pursue his passion. Climbing bums often migrate between destination areas, following the seasons.