My husbands family refers to their father by his first name in reverent and awed voices. I don’t know why and as I got to know his siblings I heard how he was very adamant about having intelligent conversations and was generally approached with apprehension but expected to be approached so that he could provide his "say"on a certain subject matter. Well that was all blown to hell when I met him and found him to be an endearing loving man that had no inclination to keep everyone around him walking on eggshells. He now insists that all the younger granchildren call him Grandpa.
I breifly worked with my mother, and called her ‘Ruth,’ and one of her co-workers said ‘You call your mother by her name’ and I said ‘No, but I assumed you did.’
Mom and Dad… if I called them by their given names, I’d be ignored until I said Mom or Dad…
Hey you didn’t work too well either 
My aunt and her family (my cousins, and even my grampa!) have a signal whistle, that they use to announce they’ve arrived or their position. My mom whistles to them too, and also has a special whistle to which I respond.
I also respond to aunt’s whistle, which is strange because when I hear it, I turn my head immediately even if I know there’s no way they could be near me.
My dad doesn’t like being called “dad” and prefers to be called by name. This would be fine, if his name weren’t Richard, and he prefers the nickname ‘Dick’.
You have NO idea how often my friends have asked me “Uh, did you just call your dad a dick?”
I’ve always called my parents “Mom” and “Dad”. Well, sometimes I call my mother “Ma” or “Mo”. My father was always “Dad” or in a hurry, “Da”. Asking for them on the phone, I always used their first names, and occasionally when trying to get their attention. I remember being very weirded out as a little kid to find out my parents had actual names, and that “Mom” and “Dad” did not appear on their birth certificates.
I had a friend who called her parents by their first names. She was adopted at a few months old, but around age 16 or so, she decided to start calling them by their first names. This caused a lot of tension in their family, but I think they’re okay with it by now. (Don’t know though, haven’t talked to her in years.)
As for teachers and such, I could never call one by their first name. It would feel so disrespectful. I don’t even like calling strangers by their first names, especially if they’re older than I am. It’s always “Mr. ____”, “Mrs. ____”, “M’am”, or “Sir”. Or a professional title like “Dr.” or “Professor”. I feel slightly weird when random strangers address me by my first name. First names, to me, are for close friends and family.