The halacha on nicknames, is talking about things like bozo, klutz etc.. (i know someone whose off the derech now, his nickname was bozo, he happened to be a very nice guy, it just stuck with him)
which if the name sticks even if the person says they don’t mind, they do, the person that started it will have a lot of explaining to do upstairs (or down)
it was never about avi or if you call a loved one darling etc..