Clothes that can be described by one or more of the following examples:
1) Only putting on the most necessary clothes when going for a ride in the car. For instance when you are going to 7-Eleven to fill up the car with petrol etc. And then right back home again.
2) Clothes that you haven't mirrored yourself in.
3) Sweats/sunday clothes.
Plausible examples, in everyday conversations, were the expression could be used:
1) "Honey, will you please go and fill up the car, it's almost running on empty!". "Sure hun', let me just get on some car clothes".
2) "Wow man, have you looked yourself in the mirror before going out today? You look like shit!". "No need my man, these are just my car clothes".
3) "Ahh, another Sunday in my favourite car clothes".