N.
I disagree with the previous poster in that I don't think your husband is ENTITLED to make an ugly remark about anyone else, regardless of his circumstances. I do agree, however, that he was probably just saying the thing he thought that anyone else would say, and it may have been out of some frustration regarding his sister. I do not think his remark was malicious in nature though, and definitely not directed towards you, so I wouldn't make a big deal out of it. I think your response was sufficient to bring the insensitivity of his remark to his attention and it's doubtful he would say something like that in front of you again.
Blessings,
N.