Women may be teased about small breasts, but for a man, the whole 'masculinity' myth is inexorably tied into the size of his penis. As stated previously a larger penis has been viewed as a sign of sexual prowess and, more importantly, virility, hence the culture of 'size' which even now men find impossible to escape.
Women may be teased about their breast size, but in any way that links to their ability to bear children - that would mean that narrow-hipped women would be scoffed at by their broader-hipped sisters, which of course does not happen.