My husband calls his dad “Pop” sometimes. Both when referring to him and to his face. He also calls him “Dad,” but I think “Pop” is more frequent.
His (husband’s) brother does the same.
FTR, the huz and BIL are 39 and my FIL is 59.
The same with me. Neither he or I were embarrassed about it. He passed on seven years ago. How I wish I could still call him “Pop.”
Damn it, now the tears are starting to come.
My dad’s dad has been gone now for twenty-four years. Still when my dad leaves the graveyard–“See ya later, Pop.”
Every time.
Pop seems more American to me, at least for your Dad rather than Grandad.
Round here, Dad is by far the commonest term, but ‘my old man’ is also really ordinary when referring to him in the first person, as in:
My old man’s a dustman
He wears a dustman’s hat
He wears gor-blimey trousers
And he lives in a council flat.
My husand calls his father Pop, but not exclusively. He uses Pop and Dad more or less interchangeably.
My grandfather also called his father Pop.
My hubby and his sibs all call their father “Pop”, even the oldest ones, who are not my FIL’s biological kids. The oldest ones call FIL “Pop” and their bio father “Bill” (or more commonly “The old bastard”, but that’s another post!)
I call my dad “Poppy.” As in, “I love you, Poppy. Thank you for the birthday present!” If I’m referring to him in conversation to other people, I’ll usually call him “my dad,” but sometimes “my poppy” slips in.
I call my Dad “My Pops” sometimes when I’m talking about him, but call him Dad when talking to him. I think I’ll give “Pops” a whirl next time I talk to him. It’ll crack him up. Good thinking DMark!
I dated a guy who always referred to his Pops as “My Old Man” when talking about him, but again, called him “Dad” to his face.
My boyfriend calls his father pop. I’ve started doing it too.
I call my father a number of things and none of them are terms of endearment.
My CT cousins call their father Poppy. We lived with them for a short time when I was very young and it stuck for us too. He has been Poppy to my sisters and me for as long as I can remember. I used to think it was his name. It wasn’t until very recently that I realized it’s what his kids call him.
Every once in a while, I’ll call my father daddy when speaking about him. It REALLY annoys me but not because it’s embarrassing. It’s because he is NOT my daddy and never will be. Daddy needs to be earned.
My mother always has been and always will be mommy and she earned that name. Of course, I still occasionally call her Mommy Dearest when I want to annoy her. 
I call my dad pop sometimes. I dunno why. I dislike routine.
As a teenager, I used to refer to my father as ‘my old man.’ I disliked him so intensely that I avoided referring to him as my father; I didn’t want to actually acknowledge the relationship.
I mostly called my father Daddy, but from time to time I would call him Pops…usually during light-hearted greetings or conversation. We used to call my father’s father Poppy.
Everyone who was a direct desendant of my uncle called him Pops, kids, grandkids, etc. I called him Uncle.
Never called my father “Old Man” or “Pop”, nor do my children address me that way. However, I do sign my emails as Dad or Pop - just because…
Yes, I knew one of these guys, a late '70’s version, though - mullet, gold chain, and disco shirt! He also referred to his 20-something wife as ‘the old lady’, as in “the old lady flipped out when I got home at 4 a.m. last night”.
My grandfather (born 1909) and his siblings referred to their parents as Mom and Pop. That’s probably the only time I’ve heard Pop used for real. I have heard “My Old Man” from people as young as their 30s, but generally not from younger people.
I have been calling my dad Pops for a long time. Not sure why but usually only when we are working on something together. I normally address him as dad when others are around but when it is just us together it morphs. When we are working on something it will be “ok, What’s next pops?” or “great sand wedge pops” when golfing.
I never knew my father, but everyone in my family called mom’s father “Poppy”, including his other children. Like wise her mother was “Nanny”.
My father’s parents were “Gram” and “Grampa”.
My older siblings refer to our father as “Daddy”.
I’ve known many people who call their father “Pop” or “Poppy”. “My old man” is generally a term for one’s husband or long-time “boyfriend”, in my experience.
I live in NY and am of mixed Irish/Polish/French/English ancestry.