If you look at the video, Will Smith was laughing at the joke himself, until he saw her not laughing. I don't feel sorry for her she's a tramp if you read her bio. She's got Will Smith by the gonads and he's hen-pecked while she sleeps around all the time. Sometime back she got caught with her son's best friend. Their marriage is a mess and always has been.
Chris Rock generally is a Class Act, and really didn't know that it wasn't a style that she was wearing. He had no idea about her disease, it was an innocent joke.