As Judgers, INTJs are more likely to dress properly. But as INTs, they are likely to be detached from the physical world and may fail to see any point in dressing properly. It's a mixed bag for this type, but they do tend to dress better than their muddled NTP cousins.
There's also a characteristic INTJ facial expression, aka "the Death Glare." I couldn't explain it better than this writer, so trot over to her site and read her little article.