Respect shouldn't be earned, it should be an implicit part of any human interaction. Now, if you are dealing with a person who has proven themselves to you in the past as being a turkey, then factor that into your interaction accordingly. But interactions should start with respect. I teach high school, and I see a lot of kids who give no respect to any adult on campus, and hide behind the excuse of "respect has to be earned". But that's not reality. If I met your grandmother, I'd be respectful to her even if that was our first interaction.