your probably looking for a guys answer, but I felt compelled to write this. if a guy doesn't like you at your worst, he doesn't deserve you at your best. think of it this way, that means you can be comfortable with him now, you won't feel like you always have to impress him.
I would see a girl dressing sloppy. It's not a bad thing. I sometimes go to the store or classes in a hoodie and pajama pants if I am running late. Nobody expects you to look good all the time. As long as you know how to clean up, then I have no problem.
My husband said he liked it when I dressed down because it showed him I was comfortable being just me around him, without the pretty hair, make-up, and fancy clothes. I think a lot of guys actually like seeing the girl behind all that. But, I'm not a guy so I couldn't really say :-)