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.