See mutual followers / people we follow

When looking at someone's list of followers or people that person is following, I would like to be able to easily see our mutual followers / people we're following, either by sorting those people to the beginning of the list or via the click of a button. That way, when someone adds me and I'm not sure who they are, this list of "mutuals" can act as a trigger for me: "Oh, right, I met them when I visited so-and-so" or "hey, those are a bunch of ARG folks; this may be the beginning of a new ARG!"