How is a scar private if others can see it?
a facial scar is one thing you should ask them about because they would be ofended if a little kid made fun of it and it was part of their past they left behind. but some things you don't know like do they not drink because they are in a.a. or did they go blind from a o.d. you would have to wait for them to tell you about when the time is right.
If it is a really bad scar then the person may not want to relive the moment that caused it. If they want to talk about , they will tell you without you asking.
So......been in a knife fight lately? That would break the ice nicely....