If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.
I was assuming that by "interact" in the great-grandparent you meant more substantive stuff than passing each other on the street. If you weren't, my point still stands: Bayesian logic requires one to have an opinion about strangers passing in the street, but only in the way it requires one to have an opinion about the triple point pressure of copper.
And hope they don't mug you as you do, for starters.