My Mum had this rule so we called everyone Auntie and Uncle.
Even next door neighbours.
Other kids in the street laughted at us.
It was also very awkward in my teens when I felt stupid calling random people Aunt and Uncle.
Several of them asked me to drop it now as I was almost an adult and that took a while to get used to. Felt wrong just calling them by their names.
So I decided that we would not go down the same path with DD.
We then did have someone I'd never met before introduce herself as 'Auntie X' to dd recently, as she said it was rude for a child to just call her X. I felt wrong about it - to me, Auntie is a label either to denote a (blood, or adoptive) relationship, or a special bond that someone has. It's not a label for anyone off the street. I was a bit p**d off about it but as we are unlikely to see them again I didn't give it too much head space.
I haven't been Auntie or Uncle to any friend's kids either, despite having an extremely close bond with one particular family. They don't respect me any less, or mess me around any more, and I don't love them any less for them calling me by my name.
YABU.