Mrs. Hypothetical

A woman sees a man and becomes so infatuated with him that she practices pronouncing or signing her first name with his last name, or even "Mrs." plus his full name.

Less commonly, men do this with their girlfriends' names.

Averts The Maiden Name Debate.

Anime and Manga

 * Happens in Ranma One Half during the Soun/Hinako arc with Hinako writing her name as Hinako Tendo on the school chalkboard.

Film
"Susan: I'm not getting any of my mail, nothing has been filed. Ever since she got engaged, my life has been a disaster. She spent the last three months writing down her married name. "Mrs. Judy Hicks", "Mrs. Donald Hicks"; "Mrs. Judy Mitchellson Hicks", sometimes with a hyphen, sometimes without a hyphen. Sometimes, she spells the hyphen."
 * In Mean Girls, when Regina wants to convince Aaron that Cady is a psycho, she lies that Cady writes "Mrs. Aaron Samuels" all over her notebooks.
 * In Big, Susan complains about her recently-engaged secretary doing this all day long:

Literature

 * Pride and Prejudice: Lydia leaves a note when she elopes rejoicing over how the next time she writes, she will sign her name "Lydia Wickham."
 * The narrator of Wuthering Heights first becomes interested in the story of Heathcliff and Catherine when he finds evidence of this trope in Catherine's old room.
 * In the Vorkosigan Saga book A Civil Campaign, after, he begins writing her name in excess on loose sheets of paper,.
 * In Stephen King's IT, Ben Hanscom thinks of Beverly Marsh like this at one point early in the story.
 * Little Women: Jo realizes she is in danger of, as she sees it, losing Meg when she finds out Meg has been scribbling "Mrs. John Brooke."

Live Action TV

 * ICarly: Sam calls Carly and Freddie 'Mr and Mrs Benson' in iSaved Your Life.
 * Carly in iDream Of Dance: "If he's a nub, then someday I want to be Mrs. Carly Nub."
 * Sam in iPie: "Why can't I marry this pie? All I want out of life is to be Mrs. Sam This Pie."
 * In iParty With Victorious, Carly imagines herself as Mrs. (Steven) Carson, writing "Carly Carson" on the computer in various fonts.
 * Rachel's friend Mindy does this in Friends: "I want to be Mrs. Barry Farber, DDS."
 * In Lois and Clark: The New Adventures of Superman, Lois briefly considers taking up the name Kent after her marriage to Clark. She takes Clark's nameplate from his desk at the office and covers the "Clark" in "Clark Kent" with her own nameplate to see how "Lois Lane Kent" would look.
 * On The Brady Bunch when Marcia develops a crush on her dentist, she imagines life as "Mrs. Marcia Dentist."
 * In The Big Bang Theory, when the guys are watching America's Next Top Model, Howard keeps pointing out which of the contestants is "the future Mrs. Wolowitz". Of course, being Howard, "the future Mrs. Wolowitz" is pretty much every contestant.
 * Anya sings a whole song about becoming Mrs. Anya Christina Emmanuella Jenkins-Harris in the Buffy the Vampire Slayer episode Selfless.
 * This is also partly a callback to the name she made up for when the Watchers' Council was investigating Buffy's True Companions, and she was afraid they would find out she used to be a demon.
 * In Neighbours, Tad Reeves develops a crush on Susan Kennedy and is caught writing 'Susan Reeves' over and over again in his exercise book. Oh, and Susan just happens to be his school principal.
 * In the Doctor Who episode Blink, upon meeting Detective Inspector Billy Shipton and being told of the mysterious disappearing vehicles at Wester Drumlins, plucky girl detective Sally Sparrow fumbles and switches his surname for hers, identifying herself as Sally Shipton. It's played as an unmistakable sign that she's into him.
 * Played for laughs in Happy Endings with Penny after she meets the unfortunately named Doug Hitler.

Newspaper Comics

 * In Garfield, Jon takes the thought process to a ridiculous extreme when he ponders what Liz's name could be if they got married: "Mrs. Jon Arbuckle, Mrs. Liz Arbuckle, Mrs. Liz Wilson Arbuckle, Dr. Mrs. Liz Wilson Arbuckle," etc.
 * In an early Peanuts strip, Violet tries to imagine being married to Charlie Brown and says, "Mrs. Violet Brown..., Nope, I just can't see it."
 * In a later strip, Sally imagines herself as "Mrs. Sally 95472" and delivers the same punchline.
 * Beetle Bailey: One of General Halftrack's officers is mildly disturbed to find a notepad with "General Amos Buxley" on it.

Sports

 * While serving as a commentator on WWE Smackdown, John Bradshaw Layfield would refer to Michelle McCool as the "next ex-Mrs. Layfield".
 * When the German national soccer team went through a series of coaches in a rather short time period, the host of a comedy show joked about the decision on who would be the next coach. "What's his name? Our future ex-national coach? A yes, Christoph Daum." Hilarious in Hindsight, as Daum really lasted only a few months.

Theatre

 * In One Touch of Venus, when Venus first hears Rodney Hatch say his full name, she repeats it to herself, then adds "Venus Hatch" to test how much she likes the sound.

Western Animation

 * Seen in Fiona's childhood diary in Shrek 2: "Mrs. Fiona Charming" (as in, the wife of Prince Charming).
 * Though Charming is shown to be his first, or even only, name, so it's unlikely she'd actually be called that even if she did marry Prince Charming.
 * Played with in Mickey, Donald, Goofy: The Three Musketeers: a lovestruck Minnie writes "Mickey and Minnie Mouse" in her notebook, and then notices that they already have the same last name.