I can instantly tell by the outside of a wedding invitation if it was sent by the Brooklyn side of my family or the Lakewood side. Personally I find it utterly ridiculous to be addressed as Rabbi, but if that's the worst that can happen I can live with it.
You address someone as Rabbi if they
a. are an actual Rabbi (in a shul, chinuch, whatever),
b. they're a serious and/or well known talmid chochom, or
c. they need it to feed their ego (#ChessedOfTheDay)
For anyone else, דריי נישט א קאפ.