Once upon a time I was buying some SLR lenses from a Craigslist posting. Dude and I exchanged some phone calls about the price and condition and setting up the meeting.
About a week later Facebook started suggesting some random name as a connection. The name was vaguely familiar, but I couldn't place it. Then it occurred to the that random suggested connection had the same last name as Dude! Sure enough, it was his son.
The moral of the story is that the Facebook app trolls your call history for connections. That's too evil for my taste, and the app has been removed ever since.
To be fair, the app did ask for permission, but I always said no. But it would keep asking and keep asking and I eventually accidentally touched the wrong response. And while it claimed I could turn that feature off at any time, I never found the preference.
Like I said, I removed the app, and haven't really missed it.