A person who will only wash once a week. During this week you can see them slowly turn more filthy each day until the fated day of the week were they think it is reasonable that they should get a shower. One Week Washers will also argue to others that being outside in the rain is also like getting a shower since it is basically the same principle, but it isn't.
Fred: Mike, each day I see your hair getting more greasy and your armpits getting more smelly, get a shower!
Mike: But I got one 6 days ago, I'll get one tomorrow and it shouldn't be that bad, it was raining yesterday while I was outside.
Fred: Ugh... One Week Washer!