For me it's not about whether you're on the back of a male or a female, it's knowing you are putting your life in their hands and you have the trust and belief in them to keep you safe. And yes I've been pilly for some real nutters but only because I've trusted them implicitly.
After all these years riding my own bike and being pilly as well, you tend to get an inkling about someone's skills the first time you see them ride their bike