This came up in a post here regarding names and in-laws, and also recently came up at work and I started thinking about it in my own life.
How do you address your in-laws? Do you call them "Mom" or "Dad"?
I address someone by how they
introduce them self to me; if you give me your full name I'll use that, even if other people use a nickname. I work in a hospital and even though most of
the nurses address the intensivists and residents by their first name, I
still address them as "Dr.XYZ" unless they tell me otherwise. When I
was a kid, I had a couple of friends who addressed parents as, "Mr. and
Mrs. XYZ" but I was never taught this by my own parents so I often used
their first name, if I knew it. Now I look back and wonder if I was being rude? But not all my friends did this either, nor did I have my friends' parents say, "Call me X". I feel awkward with the distinction between calling someone Mr. or Mrs. XYZ vs. their first name; in academic or workplace settings it seems obvious to me, but in real life, I think it gets tricky.
My MIL has never said one way or another, so I address her by her first name. FIL actually told me to call him "Apu", which is Hungarian for dad. DH does not call him this, he calls him Dad (as does SIL). DH does not call my parents Mom or Dad.
Calling FIL "Apu" makes me a bit uncomfortable. Partially because I feel silly about pronouncing it incorrectly, and partially because he's not my dad. For the most part, I usually avoid this by not directly naming him when I address him, for example, I'd look directly at him and ask, "Can you pass the peas?".
In Canada, FIL uses the english form of his name, and for his common acquaintances, they call him by the short form of his name. I could try calling him this and see if he corrects me, but I know he is easily offended by things. He's very old fashioned and might see it as an offense that a younger person was calling him by his first name or a short form. He's already gotten offended at BIL who's children were calling him "Papa {short form of name}"; he felt they should be addressing him by his full name. Us "kids" are still confused about exactly how he wants his grandchildren to address him.
I could also just suck it up and call him "Apu" since it's is a word that does not hold particularly meaning to me and realize FIL is definitely not going to change his ways. But I think the topic is interesting- "what's in a name!". To some people, a lot.