I think about this. Most days I wear work clothes. That will be well worn, and possibly dirty, jeans. Work boots stained from grass and dirt, a bandanna and dark safety glasses. A flannel shirt, untucked, or just a whit tee shirt during warm weather. With my work chances are it will look dirty after work. I figure if i was just sitting outside the Safeway some people might hand me money! BUT, when I'm up and about I'm MOVING. I walk with purpose, with my head up, shoulders back, and alert!
Not sure if people think dirt bag when they look at me or not? Don't care much, and I'm not going to come home and clean-up just to drop into Safeway to pick up some pork chops for dinner.
I don't think twice when I see someone dressed like that, in fact, I'm often led to think "that's someone who worked their a$$ off today" rather than "why didn't they clean up before coming to the store?". As a guy who used to carry the tools for a living, I often came home dirty, sweaty, sometimes muddy, wet and cold. While I don't do that any longer, I respect those that work hard and that's what they have to show for it - regardless of what they do for a living. Heck, I've met my fair share of 'clean and nicely dressed' folks that were outright D-bags. They say that clothes make the man, but I find that's not always the case.