There’s a moment in the movie “Analyze This” when Billy Crystal's character asks his soon-to-be father-in-law if he can call him by his first name and he replies: “My friends call me Captain.”

The look on Crystal’s face captures perhaps everything a prospective son- or daughter-in-law feels when facing this crisis.

What do you call your new in-laws? Mom? Dad? Mr. and Mrs. So-and-So? Captain? And why does it feel like the rules are changing?

Related story: In-Laws 101: 5 Questions to Ask Your Spouse-to-Be

Traditionally, "Mom" and "Dad" were what you called your new parents-in-law. This was determined through solid scientific research; I asked my parents.

My mother — marrying at the age of 23 into a predominantly Italian family in 1967 — called my paternal grandparents mom and dad, though even for her generation it did take some adjustment.

“In the very beginning it was awkward. [At first] I called her nothing. I didn’t say ‘Mrs. Altiere.’ I would just say ‘Hi, how are you doing?’” my mom said.

My parents dated for a mere six weeks before becoming engaged, so even when married five months later, my grandmother still was a virtual stranger. And yet the "mom" title didn’t take long to emerge.

“It was just what you did,” said my father, 68, who called my maternal grandparents mom and dad immediately upon being married — a fact that raises certain questions. If you are going to start calling the in-laws mom and dad, when do you start? When is it appropriate to phase out the formal and enter the familial?

Leah Shifrin Averick, a Chicago-based therapist and author of the book “Don’t Call Me Mom: How to Improve Your In-law Relationships,” says there really is no right answer.

“It’s important to take the initiative and do what’s comfortable for you,” she said. “There’s no consistency — it’s always awkward at first.”

The issue of in-law addressing goes to the very core of child psychology, Averick said.

“The most precious words in any language to a child are mommy, daddy, mom, pop, etc. Some people may feel it’s disloyal to their own parent to call someone else mommy and daddy," she explained.

“It can be hard when a parent is lost or it can be hard when you’re particularly close to your parents — or when you’re particularly not close. It’s a very complex issue with no right answer."

And it’s not just the "kids" who might feel strange about using such treasured names for their in-laws.

“For parents to hear someone else be referred to as mom and dad is uncomfortable — there might be a bit of jealously there, too," Averick said.

On the opposite side of the spectrum are the new in-laws who have no interest in being addressed so intimately. Averick says one woman she interviewed had an attitude like, “I have enough children, I don’t want [my daughter-in-law] to call me mom.”

But that doesn't mean she doesn't care for her daughter-in-law.

“How you feel about [your children-in-law] does not reflect what you call them, and what you call them does not necessarily reflect what you feel about them," Averick said.

New York City resident Kristin, 31, said she was surprised and a little bit hurt when she asked her mother-in-law if she could call her mom and she said, "No, call me by my first name."

"I just assumed you called them mom and dad because that's what my parents did. My husband said I was a dork for asking," she said.

More scientific research: My brother-in-law, 29, who married into a Japanese family, had two weddings — one in Japan and one in America, and he decided to start calling his mother-in-law mom between the two.

When his mother-in-law’s flight arrived from Japan, he “hugged her and called her okasan.” Why? "To create that sense of family. It wasn’t just out of respect — I didn’t think about that. I guess it was more emotional," he said.

He hasn’t yet started calling his father-in-law dad, though he can’t put his finger on why. On the other hand, his wife, Yukiko, 25, has very specific names for his parents and very specific reasons for using them.

“I feel awkward to say just the first name,” she said. “That’s why I say ‘Bob-san’ and ‘Bonnie-san.’ I want to be polite.” She explains that in Japan, ‘san’ is an affix affirming respect.

The question of respect can be very much a part of the issue of in-law addressing — particularly in more traditional cultures.

During her research, Averick conducted her own interview with a Japanese man, asking him what he likes about his daughter-in-law.

“He said, ‘She’s very respectful. She doesn’t call us Mr. and Mrs., she doesn’t call us by our first names, she calls us mom and dad.'"

This issue is nothing new. The question of what to call the in-laws exists in even the most primitive cultures. James George Frazer, the social anthropologist of the late 19th century, talked about it in the seminal exploration of ancient cults, rites and myths, "The Golden Bough."

According to Frazer, for the New Guinean dyaks it was a curse, a serious taboo to pronounce the first names of their in-laws.

Different cultures have different ways of dealing with this issue of how to be familiar without sacrificing respect.

There’s a tradition in the American South of taking a person’s first name and adding Miss or Mister to it, as in Miss Abby or Mister John. This accomplishes two things: It avoids the too-familiar first-name basis, while at the same time suggests a certain intimacy that “Mr. Surname” and “Mrs. Surname” doesn't. One might call it the First-Name Basis Formal Tense.

Other social segments have their own approaches. New York City resident Weston Almond, 35, who spent his youth attending society functions and debutante balls, says his mother wanted his wife to call her mummy (she also wants her grandson to call her mimsie).

According to Averick, the best way to address the issue of what to call the in-laws is just to confront it head-on. She gives credit to her first daughter-in-law, who simplified the issue by just asking her what she would like to be called.

Duh. Why didn't you think of that?

Related story: In-Laws 101: 5 Questions to Ask Your Spouse-to-Be