No, sorry, that is just not on. Its not just happened the once...what sort of message is that sending to the kid?? Either your parents are so disorganised/useless that they can't get you dressed in the morning, or you put up a fight and we cave in...neither of those possible explanations is acceptable.
Unless there are serious health/mental heath issues, or there are a million kids (which I understand is not the case) then he should be dressed.