Not the person you're replying to, but I had a boss at an old job who liked to make "your mum" jokes as often as humanly possible. It got annoying. Since we worked in forensics and did a lot of OSINT I decided to stop it using Facebook.

Found his Facebook. He didn't have any family listed, for privacy. Friends list wasn't visible either. However his dad and sister, both easily identifiable as such, I found since they had both liked the same profile picture a few years ago, and I could view their relationship (handy trick, go to someones user account, add ?and= followed by the user ID of another user and you can view relationships between anyone). Saw that they had a few mutual friends, <10. Found two which fit the criteria for possibly being my boss's mum. Searched both names in the electoral register and got rough locations. One of them lived in the same city my boss had listed as his birthplace, and co-habited with the person I previously identified as his dad. She was using her maiden name on Facebook (there goes security questions). I paid £1-2 for the full address.

For the next week or so I sent him random bits of information about his mum whenever he made a bad "your mum" joke at me (if it was good I didn't particularly care). Previous addresses, streetview screenshot of her house etc. Despite streetview blurring her car's license plate, I could see what make/model/colour it was, which was enough to find the license plate by skimming through photos posted on various sites which let you search by location. So I sent him MOT and road tax reminders too. It was fairly easy to find what schools she had gone to, previous marriages, a company she had started etc. He stopped making "your mum" jokes after a week.

Bear in mind: this was someone who worked in computer security and was actively privacy conscious, and within an hour I had enough information that I could have probably stolen his identity.

I like to do it passively if the person doesn't already expect it. Like asking overly specific questions about past events they posted. 'how was dj dickhead in January?' 'the girl you were with didn't she go to (put school I surely shouldn't know anything about here)' just making random creeper comments and getting worse until I explain my intention. For the best effect stretch this process over a evening or more.

We had a overly 'social' secretary which didn't understand privacy implications until she met our team :) we pointed out every joint, cheap vodka bottle, or even slightly awkward things found in mirror selfies until she started to really rethink her privacy.

Or there is a old social network many people in my country kept for the email. They encouraged to write or at least post poems. Lot of awkward lines to be found there to make some heads red.

While I don't approve of some (most?) of their antics, Phone Losers of America did a series where they "prank called" users of Foursquare and started reading off details about their personal lives. Pretty scary stuff that puts things in perspective.

I am thinking things like Wechat, Telegram (also Whatsapp to some degree but that's behind in functionality) but also things like discord and slack.

So without a direct social graph, specialised interest groups, more direct connections, more 'privacy' at least in terms of how public the data is available.