It depends. If that friend actually knows my parents, I just say “Mom” or “Dad.” They know who I’m talking about. If they do not know them, I add the qualifier, at least with the first reference in the conversation. Then I just use the name, having already made the distinction.
Another way to think about it is that the OP’s (ad some others’) objection to my saying, “Mom is coming to dinner.” is a bit insulting. He’s objecting to the name I choose to use for my mother. He has no real right to object to the name we’ve decided by which I refer to my mother. I would never say “Mother is coming to dinner.” or “Mama is coming to dinner.” because those are not the names I use for her. I would say “My mother is coming for dinner.” because “mother” is a designation or title. I might say “My mom is coming to dinner.” because then I am using “mom” as a designation or title not a name.
I don’t say "Sister… " or “Wife …” because those are not names I ever use to refer to thosoe people. How dare you object to my choice of nicknames. 
In fact if you look up in English usage books it tell you to write. “Give the book to Mom” and give the book to my mom." precisely because the firs “Mom” is a name and the second is a designation.
Or in my case, I had sex with YOUR dad last night. :eek:
If I’m speaking to any person who does not actually call my mother “mom”, then I say, “my mother” when I am referring to her. If the person I am speaking to also calls her mom, then I say mom.
Which is the prefered phrasing?
The Zombie ate my Mom’s brains for supper?
Or: The Zombie ate Mom’s brains for supper?
Quite interestingly, I began thinking about how this kind of situation would play in my native language (Spanish) and I realized that, to me, having people say “my mom” or “my dad” (in Spanish) would sound real weird!
I guess it has to do with how Spanish works. For instance, if I want to say “my hand hurts” in Spanish, I would say “me duele la mano” (gloss: “[1st. person reflexive pronoun as OD] hurts the hand[subject]”). “Me duele mi mano” sounds weird and borderline ungrammatical. We are not big when it comes to using possessive pronouns.
I have realized that, in my experience, when somebody speaks about their own father or mother, they will always just say “mamá” or “papá”.
“Mamá viene a cenar” = “(implicit “my”) mom is coming for dinner”.
“Papá se puso enfermo” = “(implicit “my”) dad fell sick”.
Saying “mi mamá viene a cenar” or “mi papá se puso enfermo” sounds positively strange and borderline antinatural to me.
CAVEAT – This may well be an artifact of how we use Spanish in my region. But this is the kind of language I grew up with. Or something.
Quite an interesting effect! To the OP, in English, not using “my” sounds strange and irritating. To me, in Spanish, using “my” sounds antinatural and weird.
Ah, humans are strange, I guess
If the zombie ate the brains of more than one mother, it would be “The zombie ate moms’ brains for supper.”
Argh…the responses to the OP are 50% as annoying as the OP’s OP which gives crediblity to the number of people who refuse to use a modifier before “mom” or “dad”. I agree with the OP that there is a self-centeredness to phrasing it without the modifier. It is possible to forgive those individuals who are not your sibling but are so close to you and your family that your mother/father was like a surrogate mother/father to him or her but otherwise it is just boorish and egocentric. The people who are usually leaving off the modifier in polite conversation are most often the ones that you barely know or see that often and for whom you have never met his or her mother or father (his and her are also modifiers)…so, please, just be kind enough to the 50% of us who find the overly familiar and irritating “mom” and “dad” references annoying and address the person you are talking about with appropriate language just as if we have never met “your” mom or dad…because in all likelihood we haven’t.
Yeah, my advice is to suck it up. Or have I erred all these years in assuming my audience has the brainpower god gave a potato to know that if they’re not my sibling, the mother I reference must not be their mother?
Okay…time to suck it up as suggested for all “mom” conversationalists and in this case, happen to be two people who don’t know each other that well…
Jane: Mom is coming over for dinner. Mom loves my lasagna.
Mary; Oh that’s great. Mom came over last Sunday and had a lot to say about my choice of cream sauce for the angel hair pasta versus the usual red sauce.
Jane: I hate when that happens…trying to surprise Mom has never worked for me; I use Mom’s recipe for lasagne and never substitute…though I’ve been tempted to shake up the sauce ingredients…she’s a tricky one though…Mom will catch it every time.
Mary: Mom’s taste buds seem to be inconsistent lately; not sure if it’s age or what but there have been comments made recently about my cooking and nothing has been added that Mom hasn’t had in the past and loved.
Jane: Mom can be really fussy about my lasagne too…her palette is the same as it always was.
Mary: No, Mom’s palette is changing. I know it.
Jane: No, Mom has the same sense of taste that she has always had.
Mary: How do you know?
Jane: Because she’s my Mom.
Mary: No she isn’t…she’s my Mom.
Jane: We’ve been talking about my Mom.
Mary: We’ve been talking about my Mom.
Ok…eavesdroppers and other “Mom” sufferers…let’s just suck it up.
“Mom,” capitalized, is a name. It is used to address the speaker’s mother, or to refer to her with a third party, in which case it is always understood to refer to the speaker’s mother. (It should have been clear to Mary and Jane, as it was to me, that they were each referring to their own mother.) Or, it is occasionally used as a nickname for an unrelated person, in which case it works just like any other name.
“My mom,” uncapitalized, indicates a person by relationship, to a third party.
“My Mom” is incorrect; the eavesdropper has made a transcription error (writing “palette” for “palate” is another 
).
Good lord…I was giving food for thought…er…and a decision to capitalize (or not) is highly irrelevant to the context of what was written; I get it, you’re in the Mom-centric corner. Seriously, your contribution to what was written was to point out a spelling mistake and an absurd distinction between “Mom” and “mom”…egads.
“My Mom” is incorrect? What 18th century book of etiquette are you referring to (can I end this with a preposition or find another work to cap off the sentence)?
“Mom” or “mom” is not a nickname; it is a title that is given to someone, bestowed on someone, socio-culturally or affectionately, who epitomizes the qualities that we have collectively agreed belong to that of a Mother or mother. Otherwise, the family could give the nickname to a brother and, when this happens, it is usually a pejorative label given to a nagging brother.
I would be grateful to any evidence that you can contribute to how “mom” or “Mom” is just a nickname and not a label of honor given to a specific individual. Your comment did not help illustrate why honorific titles such as “Mom” are so casually referred to in polite conversation in front of people who are respectful of others by not referencing their mother as the mother. “Mom” or “mom” is clannish speak and this is why other posters have referenced its terminology as self-centered.
Eavesdroppers never hear anything good of themselves, or Mom.
Yehbut what if it’s Doogie Howser asking because he can’t do an emergency neurosurge at 8 p.m. because he has to be home before the streetlights come on? Huh? Huh? What THEN? Huh?
markyb, I was attempting to present a formal description of actual usage as I understand it. I’m not making the rules.
Have you never heard anyone referred to as “Mom” who was not the actual mother of the speaker?
Peremensoe: I think that things like capitalization and so on are really off base from the OP which, at its core, was addressing the pet peeve of being in the company of people who casually refer to his or her mother as “Mom” (almost always capitalized because these are the same people who in general, start their sentences with “Mom” as in the example “Mom always says…”) versus “My mom…” as in the example “My mom always says…” The OP was an expression of a pet peeve based on being in the company of people who, for whatever reason, do not feel the need to place the modifier “my” or “our” or “his” or “her” before their referencing “Mom” and the expectation that she, as the participant in the conversation, would not take offense to this.
The OP’s illustration of a “pet peeve” eventually elicited other comments about “Mom” as being nothing more than a nickname…like “Buttercup” or “Dimples” or “Little Darlin’”. This for some added to the confusion as many of us have had a mother growing up who would not have been given a nickname like “Sweetums” et al. for which to be called…as in the child saying to his/her mother, “Hey Buttercup, what time is dinner?” (even we could probably agree that the Buttercup nickname is something that the spouse would have been more inlined to use rather than the child in the family…or agree to disagree, I don’t know).
The OP did not completely outline why she finds this irritating or offensive but I will in just a moment.
My post is written from the perspective that 99% of the time, “Mom” is an honorific title that is given to a person who exemplifies a nurturing influence in our life and is usually assigned at birth to a person who will retain this title and the respect of being our mother until her death. This is not to say that everyone is lucky to have two parents, one of whom is a “mother”, but for those who did, then the title of “Mom” is not a nickname…it is the fulfillment of a duty and responsibility that is part of a social construct.
So, not everyone has a Darren or Patricia in his or her family but almost everyone has a “Mom”; the fact that almost everyone has one denotes a kind of possessiveness about the relationship he or she had with his or her mother.
As an aside, it would be equally strange if someone always discussed her son, Darren, as “My Darren”…as it could also be annoying if that same person discussed her son Darren in causal conversation without having ever prefaced him as being her son.
But for the issue at hand, and why I personally find it irritating when someone casually discusses “Mom” with me is that, as I said, there is an inherent possessiveness to the honorific title of calling someone your Mom. Placing the “my” before “Mom” is a polite way to discuss your mother without me instantly thinking about my “Mom” or the fact that even though I have never met your mother, you have intimated that your mother needs no introduction…“Mom says so and so…” Well, she needs the introduction out of respect for the fact that most everyone else has a mother and with varying degrees of closeness and intimacy. It is a matter of courtesy but this notion will escape most eyes and, for 50% of us, our ears.
So this is where some of us cite arrogance and self-centeredness on behalf of those “Mom-centrics”. For me in this matter it comes down to recognizing that many of us hold the word “Mom” (and it’s derivatives) in high esteem (unlike Buttercup, Sweetums, Lil Darlin’) and we have a singular possessiveness about our particular experience with our “Mom”. To that end, those of us who prefer that someone place a modifier like “my” or “our” in front of “Mom” is a way to enhance polite conversation when referring to a person that most all of us have had the experience of having held firmly in our mind’s eye.
And because we want to be polite about it, we don’t usually tell the “Mom-centrics” that they have just made an assertion or familiarity that we can’t possibly ever have had with their mother. Clans have their place and clan speak is great within familiar walls; but those of us who have a more silent and private proud of our family heritage don’t expect to impose our experience of mother on you or someone else.
It comes down to courtesy; bottom line.