Mom? Dad?
Mr and/or Mrs XXXX
Or do you use their first name
Oh yes the profane names you use don’t count 
When I’m in her company, “Mom” or her first name.
When I’m not with her, I refer to her only by her first name (since it’s presumed any reference to “Mom” is my mother).
In-laws insisted I call them “Mom” and “Dad.” (They are really sweet people.) I also sometimes call them by the pet names their grandchildren call them, because I’m still a little uncomfortable with Mom and Dad. When I’m not with them, I always call them “mr. hunter’s parents.”
My parents were kind of ambivalent about the whole thing, and so was my husband. They were weirded out by him calling them Mom/Dad, and “Mr. and Mrs. Raspberry” is too formal. So mostly he doesn’t call them anything (You can get by in a remarkable number of situations without directly addressing someone, especially since I’m usually around and he can nudge me: “Did your mom mean to turn right?” “Mom! Did you mean to turn right?”)
I call my MIL and SFIL by their first names, because that’s how she signs e-mails and birthday cards to me.
I call my SMIL and FIL Mom and Dad, because that’s how she signs e-mails and birthday cards. (Plus I really adore them, and they treat me like a daughter.)
I just use their first names.
first names
ETA: after the kids came, I refer to them more often as Gram and gramps
Ancestors.
Señor and señora. Although I address them in the Spanish familiar “tu” form, whereas the other siblings’ spouses (is there a word for that?) use the formal “usted” form. I get away with it because I’m a stupid gringo. I know better now, but I’ve already set the precedent, and there’s no going back.
First names. I’d rather use Mr. / Ms. Last Name, but what they want to be called trumps what I want to call them.
In my first marriage I never called them anything. If I needed to communicate with them I would run across the room and establish eye contact. My sisters-in-law (who were older than me and had known them much longer) used their first names but I never felt comfortable doing that.
I dated my now husband before my first marriage and never called his parents anything then. Same thing. I felt like a kid. Now I use their first names, but it was a long time coming.
Dickheads. Douchebags. Them.
Was first names, but they are now gone. I now am a MIL. I didn’t want my SIL to call me ‘Mum’ nor would he have liked that. We would have both been uncomfortable. He calls me by my first name. My daughter uses first names for her parents-in-law.
first names
…as little as possible…
I call them by their names. I think it’s disrespectful to my own parents to suddenly call people (who I don’t really know and let’s face it, don’t really like all that much) “mom” and “dad”. I still feel like that, 20+ years into marriage. I won’t want my son or daughters in law to call me “mom”–I’m not their mom; I’m their mother-in-law. And I hope I have learned what NOT to do from my own, thankyouverymuch.
What?
First names. Sometimes mom for his mother but never dad for his stepdad who is only 5 years older than me.
I always thought it was interesting that on All In The Family, Mike called Edith, “ma,” but he referred to Archie by his first name.
Not knowing what to call your in-laws, I saw this on Dick Van Dyke
Laura) What do you call your in-laws
Millie) So far I have been referring to them as “folks,” you know "It’s time for dinner folks.
Laura) What do you do when your alone with one of them?
Millie) Oh I avoid that situation.