I’ve posted about being an aunt before and you can read about my five nieces on my family page, but this is more of a separate issue that irks me.
Disclaimer: Perhaps there are different community/family/church/whatever dynamics that I have not experienced. I would certainly not want someone to never experience the joy of a family bond even if their mom, dad, aunt, brother, etc. was not blood-related. I have also had friends whose family was like a second home to me and I have had friends that jokingly walked into my house and said “Hi Mom” to my mom, but here’s what I’m thinking.
As an aunt, I would find it offensive for someone else- to call my girls their niece. It would discredit my bond with them, especially as an aunt who lives far away from them. Especially when they are young, its hard enough for them to understand that I am their mommy’s sister and that Gramma and Grandpa are our Mom and Dad, and how important those bonds are. It hasn’t happened to me that I’m aware, I just think it would make me sad.
I would liken it to someone telling a friend that they were their  “sister” in front of their real sister. “Like a sister”, would be more true. I would be fine if the girls said someone “was like an aunt to them.” I would be happy that they had so many people in their life that love them like I do. But there is something about saying someone is blatantly “your brother, your aunt, etc.” People that don’t know any better instantly relate that person to the meaning of a family bond and its not true.
Maybe I’m being petty and jealous, but just from a loving, young, cool aunt’s perspective-
parents- watch who you let your kids call family and
friends of people with kids- watch what you ask those kids to call you
And now I’m interested to see how other aunts out there and my sisters feel about this.