I have nothing to hide
medium.com
medium.com
It's a routing protocol (like IP) for mesh networks.
Perhaps commenters could suggest some other good replies.
Or SSN, etc. Sort of an identity theft angle.
Or "And do you have Facebook? GMail? I'll need those too. You've got nothing to hide, right?"
It's a bit of a flimsy argument but it still makes people think.
Usually they won't give this sort of information to a random person because they're not "The Government". Of course, "The Government" is just made up of regular people, who have their own personal beliefs/motives/etc.
Plus agencies don't have a stellar history of keeping our information secure (OPM hack, etc.).