In the episode The Shershow Redemption, Shershow is only called by his last name, and it is even used as a short hand for 'loser'. Though he ditches it and becomes Jason as he now has his life together.
Melinda: Anyway you guys, Jason's told me so much about you. Max: Who's Jason? Dave: That's Shershow's first name, that's so Shershow that you don't know that.
'Stiles' Stilinski of Teen Wolf is only Stiles. Even his father calls him Stiles.
Justified-- his given name is bizarre and apparently near-unpronounceable.
The titular character of Titus was referred to as "Titus" by everyone except his girlfriend and his father. Titus often even referred to himself by his last name.
On MacGyver, MacGyver is only called by his last name and refuses to tell anyone what his first name is (it's Angus). There are instances of even official paperwork only containing his last name. His first name is finally revealed in a dream sequence during the last (seventh) season of the show. His friends usually call him Mac.
Not exactly the same in his case, since he just hates his first name and doesn't tell people what it is. It doesn't really indicate distance.
Quincy, ME goes even farther by never giving the titular character a first name beyond an initial. Jack Klugman always answers that Quincy's first name was, in fact, "Doctor". Even his girlfriends and wife in the final few episodes called him Quincy.
Blakes Seven especially in reference to Kerr Avon. Even his girlfriend only ever called him Avon. Paul Darrow speculated that was because "Kerr" isn't a very good first name.
An interesting case because in this show because generally all the guys are referred by last name (Blake, Avon, Gan, Tarrant, Travis) and all the gals by first (Jenna, Dayna, Cally) with the rather odd exception of Vila, whose surname (Restal) is barely reference through the course of the series. Even Big Bad Servalan talks to him on a first name basis. (Nobody knows whether Servalan and Soolin are first or last names though..)
It's more than likely that Vila doesn't get the last name treatment because he's lower class than the rest of the crew.
House features House, Wilson, Cuddy, Cameron, Foreman, Chase, Taub, and Kutner. Cameron and Chase are in a long-term relationship, but are on a Last Name Basis. Only Amber Volakis is regularly called by her first name.
This can actually get confusing, since Chase, Cameron, and Wilson are all reasonable first names. It can be very easy to forget that their first names are actually Robert, Allison, and James, respectively. Even when you know it's their last names, it's incredibly easy to catch yourself thinking it's their first name.
Thirteen's full name was eventually revealed: Dr. Remy Hadley.
This was joked with in a Season One episode, where Cameron begins to call her colleagues by their first names after having read an "empowerment at the work place" book. This only confuses Chase and Foreman, who respond by saying her name with emphasis when they answer her questions.
Cameron: Are you mocking me?
Foreman: Duh... Allison.
House's team are so used to calling each other by their last names that when they found a book Wilson had given House with the inscription "Greg, made me think of you.", they immediately came to the conclusion that it must have been given by a woman. Of course, some fans may think this indicates other things...
In one episode of the now most recent season, the writers even lampshade this with the characters discussing (Eric) Foreman's and Thirteen's continued habit of calling each other by their work names.
This trope was also invoked to indicate House and Stacy's relationship; besides his mother, she's the only person on the series who regularly calls him Greg.
Once they got together Chase and Cameron called each other by their first names in private.
Wilson and Cameron have also been known to call each other by their first names from the first season.
Lampshaded by Cuddy's mother in Season 7, when she asks Cuddy "why do you call him "House"? The man's name is Greg."
The A-Team has H.M. Murdock. His first name is never even revealed, and it's rare for someone to call him by his initials. The rest of the team always calls him Murdock.
Dexter: Almost all the characters in Miami Metro, unless they're particularly close to each other (Angel Batista and Maria LaGuerta during their mariage, siblings Dexter and Debra Morgan, etc.). This sometimes leads to confusion when a character calls out for "Morgan" when Dex and Deb are both present. Subverted to great effect by Doakes to Dexter in episode 2.11 to reflect that in addition to capturing a killer, he now also wants to help Dexter by turning him in.
Interesting that except for Grissom, all the other CSI are on a first name basis.
As of the current season, Grissom is now The Ghost, but a returned Sara continues to refer to him only as "Grissom" despite the fact that they are now married. Even after they became intimate, she only rarely called him by his first name, and only ever in private.
Julie Finlay is a variation of this. Her full last name is Finlay, but she prefers to be called 'Finn'. D.B. still uses Julie sometimes, and she'll call him on it. But he's the only one she knows who does it.
Occasionally, D.B. gets called Russell, but not all the time.
In the CSI: Crime Scene Investigation spinoff CSI: Miami every main character refers to each other on a first name basis, except Horatio who always calls Ryan by his last name "Mr. Wolfe". Horatio is referred to as "H".
CSI NY has (Don)Flack and (Sheldon)Hawkes, although their first names get used sometimes as well, most often by Mac. Sometimes when a character answers the phone, they refer to themselves by last name. Stella does it a lot..."Bonasera". The superiors get it sometimes. Gerard comes to mind. Mac is an aversion of sorts,a rare example where it isn't a shortened last name, but a nickname for his first name.
Buffy and friends refer to Rupert Giles as just Giles. He even calls himself Giles on occasion. The only exceptions are Jenny Calendar and Joyce Summers (who call him Rupert), and Tara and Andrew (who call him Mr. Giles).
A kind-of example with Oz... his nickname is short for his last name, and his first name is not revealed until after he's left the show. (However, until that reveal, it's never mentioned that Oz isn't his first name.)
Angel has Gunn, who is only called Charles by Fred (especially while they dated), and Knox. Wesley sometimes did also.
LOST has Locke, whom only Ben and Jack call John (in Jack's case, as a sign of disrespect.) The Others routinely refer to the Losties by their last names, but use first names internally. The Losties use first names. The freighties (apart from Naomi, Charlotte and Miles) mostly use last names.
It seems like a sign of disrespect when Ben calls Locke "John" too.
Rousseau is also frequently addressed by her last name, and only occasionally as "Danielle," usually by Sayid.
Sawyer is seldom referred to as James. The only one who tends to call him that is Juliet, and later Locke. Of course, Sawyer is not his real name.
In season five, Sawyer takes up the name Jim LeFleur. He is generally referred to, even by some of the Oceanic survivors, by that.
As of season 6, both Sawyer and Hurley are commonly referred to as James and Hugo, respectively. Neither even have their respective nicknames in the flashsideways timeline.
A plot relevant case: Jacob wrote his candidates down on a last name basis, causing confusion among viewers and characters in regards to candidate "Kwon," which could refer to several characters. When he actually encounters his remaining candidates, however, he refers to each by their first names.
Mulder and Scully on The X-Files regularly called each other by last name. Once Scully's mother referred to Mulder as Fox and Scully corrected her — it didn't stop her though.
In the first four seasons, they'd occasionally use first names at emotional moments, but after that they just gave it up, apparently having gotten so used to the last names that "Fox" and "Dana" just sounded weird. In the second movie, they've had a Relationship Upgrade and have been living together for six years, and they're still on a Last Name Basis.
Although his boss does occasionally call him Jethro.
As does Ducky.
Jethro is actually his middle name. His first is Leroy.
Actually, the only people who have called him by his actual first name have been, to date: his father, Shannon (his first late wife), and people in his hometown.
Timothy McGee is universally referred to as "McGee" by everyone.
Except that sometimes Abby calls him Timmy.
And Gibbs has referred to both DiNozzo and McGee by their respective first names, usually after particularly traumatic events.
—To wit: "He called me Tim." -McGee
Averted for Director Jenny Shepherd, who goes by "Director Shepherd."
Gibbs frequently calls Tony by his last name, DiNozzo.
JAG had an interesting variant with Major (from season 5: Lieutenant Colonel) Sarah Mackenzie. Everyone of equal or higher rank in the office called her "Mac", and very rarely did anyone use her first name. Everyone below her in rank called her rank & last name, only rank or "Ma'am", even when they were off-duty.
Again, as stated with SG-1, this is standard military protocol and courtesy.
The Five-Man Band on Law & Order: Special Victims Unit are Cragen, Benson and Stabler, Munch, Fin, and Lake. Only Fin is usually referred to by his first name, and that's just because it's easier to pronounce than Tutuola; Fin is in fact a nickname for his given name, "Odafin".
Although there are other layers to this one, as in real life. Benson and Stabler call each other "Liv" and "El", which, being Platonic Life Partners, makes sense. Alexandra Cabot was always called Alex by everyone, and it was noted (by their shippers, unsurprisingly) that she was one of the few people who called Benson "Olivia", and, on occasion, "Liv". Similarly, everyone called Casey Novak "Casey", while they called her Replacement Scrappy "Greylek". Occasionally someone else calls Benson "Liv" - you can then be sure that the shit is about to hit the fan.
Alex Cabot was unique in that she referred to everyone by their first name - including Huang and even Cragen. Olivia isn't that special after all.
Averted by Cragen, who always refers to his detectives and ADAs by their first name (except for the aforementioned Greylek), befitting his role as Team Dad. He's the only character to refer to Munch as "John". Played very straight in reverse, however - nobody ever refers to Cragen as "Donald" or "Don", and address him by his title instead (again typical for a parental figure).
Dr. Huang is almost never referred to as "George", not even by Cragen or Benson, perhaps in deference to his role as The Shrink. On the other hand, Dr. Warner usually refers to Benson and Stabler as "Olivia" and "Elliot", and in turn, they always address her as "Melinda" (though when people are talking about her, she's always "Warner").
Bones has (Seeley) Booth, (Temperance) Brennan, (Jack) Hodgins, (Daniel) Goodman, and (Lance) Sweets. When Hodgins and Angela Montenegro (who does go by her first name) are dating, even she calls him "Hodgins." Even when he proposes and now that they're married.
Brennan usually refers to her interns by title and last name, though everyone else uses their given names. (It is also pointed out that her use of "Mr." or "Mrs." is a subtle reminder that the intern in question doesn't yet have a doctorate.) This also serves to indicate how much closer her intern/mentor relationship was with Zack, whom she did address by given name.
Booth almost exclusively addresses Brennan as "Bones" (and is the only person allowed to do so), not "Temperance", and never "Tempe"; even in the hallucination/dream she was "Bren". There were a couple of First Name Basis from Booth in season one, but none since The Teaser of The Woman In Limbo (one of the most dramatic moments of the entire show.)
Sweets is called by his first name by both of his girlfriends.
Hmm, is his name Lancelot?
Sully was another one. It's short for his last name, Sullivan.
Interestingly, when Booth's brother shows up, Brennan keeps calling them both Booth, although Angela amends the brother's "name" to "Booth Lite".
No one calls Christopher Turk by his first name on Scrubs. Not even his wife Carla to whom he has been married for the past few seasons (though really, that's nobody's business but the Turks'). Not even his Heterosexual Life Partner J.D. Kelso also thought his name was Turkleton and referred to him as such on many occasions; he was shocked to learn that his surname was really Turk, but decided he liked Turkleton better.
Kelso: [drunk] That's your first name. Turk: You think my name is Turk Turkleton? Kelso: [seeing Carla walk up] And Mrs. Turkleton! The Turkeltons!
Carla does call Turk by his first name when she's mad or when they're having sex.
Turk: Baby, are you mad when we're having sex? Carla: Sometimes...
Turk's brother calls him Chrissy. JD's brother does call him Christopher.
Rimmer and Lister in Red Dwarf. Taken to the point that when they're being affectionate (whether mockingly or genuinely so) it's not Arnie and Dave, but Rimsie and Listy.
The only time that they do refer to the other as 'David' and 'Arnold', is in the third season episode "Polymorph". But then, YMMV as they aren't really themselves, because the titular Polymorph had stolen an emotion from each(fear from Lister and anger from Rimmer).
Rimmer has such a cold relationship with his mother that she addresses him in letters as 'Dear Rimmer'.
In "Kryten", Rimmer asks Lister not to call him "Rimmer" in front of the girls ("You always emphasise the 'Rim', it makes me sound like a lavatory disinfectant"), and a genuinely baffled Lister says "Well, what should I call you?"
On Stargate SG-1, Colonel Jack O'Neill calls his civilian scientist "Daniel" but his military officer second "Carter". Daniel Jackson, on the other hand, addresses both his military comrades by their first names, which continued even after O'Neill was promoted to Brigadier General and put in charge of the SGC. Samantha Carter calls him "Daniel" and O'Neill "Colonel/General" or "sir". Teal'c is addressed by his only name, and calls Jack "O'Neill" and Daniel by his full name, "Daniel Jackson".
This is not out of the ordinary for a military situation at all, at least for Samantha Carter's situation. Daniel is a civilian (no military rank) and a close friend and thus can be referred to even on missions as Daniel (rather than Dr. Jackson, as she does in the first episode), while O'Neill is her commanding officer. It would be inappropriate for her to refer to him by his first name while on duty, and 95% of the show is the team 'on duty'. Hence the Colonel/General and sir, even though they are obviously close friends. It's worth noting that in a guest appearance on Stargate Universe, O'Neill did address Carter as "Sam." Many members of the fandom are of the opinion that "sir" and "Carter" have evolved into the characters' pet names for one another.
Daniel also called Sam "Captain Carter" in the first few episodes.
And when Mitchell came along, he addressed Daniel as "Jackson" and Carter as "Sam", and they both reciprocated. Which may be excusable in a military setting as at that point Carter was a Colonel herself.
Strangely, the first time they talk, Daniel and Cam invite each other to use their first names. Neither of them ever do.
Teal'c using full names actually makes sense, as his own people have just one (unless you consider the apostrophe a divider). In his mind, he's referring to them as befits one warrior to another.
On Stargate Atlantis, it's all over the place. Teyla normally uses John's rank in combination with "Sheppard". Rodney has only called his best friend "John" a handful of times in the entire series, preferring first Major then Colonel Sheppard, or just Sheppard. Sheppard himself uses both "Rodney" and "McKay" equallynote Of course, "Rodney" is not his first name. It's Meredith. When he meets an alternate version on himself, he's distressed that people call that version Rod, which he could never get anyone to call him. Ronon calls everyone by their surname except Teyla, who is in fact NEVER referred to as either "Emmagan" or her full name (introductions aside, obviously). No one ever refers to Ronon as "Dex". At most, he's referred to by his full name "Ronon Dex".
Meanwhile Sheppard and Weir start off with a very formal 'Major' and 'Doctor' before switching to the more intimate 'John' and 'Elizabeth' at all times, (including in front of all of their staff and superiors and their enemies, who all refer to Elizabeth as 'Doctor Weir'). John even corrects their enemy, who's holding him hostage about how he addresses her.
Koyla: "I think you overestimate Doctor Weir."
John: "And I think you underestimate Elizabeth"
All this, by the way, leaves poor fans very confused as to how they're supposed to refer to the characters.
Despite being long-time partners and joined-at-the-hip best friends, Starsky and Hutch simply do not use each others' first names, no matter how dire or informal the circumstances.
Kramer from Seinfeld. Even after his first name was revealed, people still kept using his last name. (not that people weren't enamored by his first name Cosmo when it was reveaaled) Also true for Newman.
Star Trek. Sure, McCoy and occasionally Spock called Kirk "Jim", but that's about it in The Original Series. McCoy himself was sometimes known by the nickname "Bones", but no one called him "Leonard". Sulu and Uhura's first names weren't even known for decades. Chekov had his first name from the beginning, but it was only used a few times, and, of course, Montgomery Scott was "Scotty" to everyone.
Uhura's stillisn't known: while various people have theories (for instance, Nichelle Nichols thinks it should be "Nyota", and she would know if anyone), nothing has been uttered onscreen and thus placed into canon.
In the 2009 movie she refuses to tell Kirk her first name. When Spock calls her "Nyota", Kirk asks, "So, her first name is Nyota?" and Spock interrupts with, "I have no comment on the matter."
Vulcans are an interesting case: their single (pronounceable-to-humans) name usually seems to function like a surname, making it impossible to achieve First Name Basis with them.
In Deep Space Nine, Keiko would more often than not refer to her husband Miles as "O'Brien"
In private she always called him Miles; this may be a reflection of her Asian heritage.
Appropriately averted when Odo became romantically involved with Kira and started calling her "Nerys" in private. (Well, actually, given Bajoran name order, he was switching toLast Name Basis, but...)
Garak the tailor is called 'Garak' by everyone. The reveal of his first name is actually a major plot point of one episode. Even after that episode, everyone continues to call him 'Garak'. In one episode, when he's muttering to himself, it's clear that he even refers to himself by his last name instead of his first name. In the entire show, only two people ever regularly call him by his first name: his mentor and biological father Enabran Tain (who switches between Garak's first and last name depending on his moods and motives) and Tain's housekeeper, Mila whose housekeeping duties did include raising Garak. She never called him by his last name (and a non-canon Star Trek novel does claim she's his biological mother via a secret relationship with Tain).
Notably averted in Next Gen and newer series, however. While characters regularly refer to each other by their titles and last names while on the job, it's not at all unusual for characters who are friends to refer to each other by their first names. And then there's Seven, who is always (of necessity) referred to by her first "name".
Although Seven does have a human name (Annika Hansen) which is used during flashbacks to her as a child, or when she's hypnotized to work in a power plant, or when she's using a holodeck simulation to have a relationship with Chakotay, etc. Normally, though, she insists on being called "Seven", even when the other rescued Borg use their original names. Go figure.
She mentions at one point that while she was once Annika Hansen, she's been Seven for most of her adult life, so thats how she thinks of herself. Its actually a conceit as her full "name" was Seven of Nine, Tertiary Adjunct of Unimatrix Zero-One, but when Janeway asked if they could shorten it to just Seven, she agreed, dubbing it "inaccurate, but acceptable".
Except she's no longer the "Tertiary Adjunct of Unimatrix Zero-One", having been disconnected from the Collective.
Ben: Hi, Will. Riker: Ben. How you doing? Lavelle: You call him Will? Ben: Why not? Lavelle: He's second in command of this ship, that's why not. Ben: I'm not Starfleet, I'm a civilian. When he's in here, he wants to be treated like a civilian. Lavelle: Riker? I bet he sleeps in his uniform.
Justified in the case of Jadzia Dax in Deep Space Nine, where we learn that Joined Trills take the name of their Symbiote as their surname, which replaces their original one. Only Sisko, Kira, Worf, and Bashir occasionally call her Jadzia.
In The Professionals, Ray Doyle is either called Ray or Doyle, but William Bodie is always Bodie, never William.
On That '70s Show, everybody (except Jackie, Kitty and Red though when he gets a job for the latter, Red get's him a work suit that says "Hyde") calls Steven Hyde "Hyde", and everybody (except Jackie and Kitty) calls Michael Kelso "Kelso".
Also, Hyde almost always refers to Eric as "Foreman," even to Red and Kitty. The other characters alternate between his first and last names.
In Doctor Who, the Fifth Doctor's companion Vislor Turlough was always referred to as Turlough.
Also, Mr. Saxon in the revived series. Despite his numerous mentions throughout the third series, and the fact that he had been running for Prime Minister since before that series even began, his first name is barely mentioned until the finale, by which time it's become pretty much irrelevant.
The Eleventh Doctor sometimes calls Amy Pond by her first name, but just as often calls her "Pond", as in "Come along, Pond(s)!" Possibly this is because he preferred "Amelia" and by the sixth season "Amelia" had evolved into You Called Me X, It Must Be Serious territory.
The First Doctor always called one of his first companions Ian by his second name, 'Chesterton' (and frequently got it wrong.)
(Damian) Spinelli and (Jasper) Jacks from General Hospital (though the latter is usually spelled out "Jax").
On Thirty Rock, Liz Lemon has called Jack Donaghy by his first name for most of the series, having only called him "Mr. Donaghy" or "sir" in the first few episodes. Despite this, he continues to call her "Lemon", which led to this slip-up when he tried to pass her off as his girlfriend:
Jack: This is my live-in girlfriend, Lemon. Liz: Elizabeth. Jack: Elizabeth.
Notably, Jack started out by calling Liz by her first name, just like all his other employees. Switching to using "Lemon", ironically, occured when they became friends.
Being in a low-level position and exceedingly polite to boot, Kenneth calls everyone "Mr./Mrs./Miss [last name]" or "sir/ma'am". In one episode, Liz noted that he "calls Tracy's lizard 'sir'."
(Erin) Silver from the new series of 90210. Even her mother and sister call her by surname.
A rare aversion, given its professional setting, occurs in The West Wing. The entirety of the central cast refer to one another by their first names (though "CJ" is obviously a nickname, her full name is heard numerous times). The only real exceptions are the President himself - who is occasionally addressed with his first name by either his wife or very close friends, and even then usually in private - and Mrs. Landingham.
It is strongly suggested that the reason why Mrs. Landingham isn't on a First Name Basis with everyone is because all the staff are following the President's example: when the two first met, he was a high school student and she was his father's secretary; he once tried to call her "Dolores" and she insisted "Mrs. Landingham, please" - and he stayed on a Last Name Basis with her ever since, even after becoming President.
Aside from the above flashback, the only other time the President calls her Dolores is just before she dies, asking her if she had ever bought a new car in her life.
Sex and the City— Carrie was usually on a first name basis with her boyfriends through the years (with the exception of No Name Given Mr. Big) but for some reason referred to Jack Berger by his last name only.
In Dharma and Greg, Greg's father Edward always referred to Dharma's father Larry as "Finkelstein".
Alias — Since everyone's in the CIA, most of the characters in Alias go by surnames — Sydney calls the male lead "Vaughn" even while giving birth to his daughter. This meant that his short-lived Season 3 wife earned a double take from the audience every time she called him "Michael," seeding distrust and dislike of the character well before her reveal as The Mole.
Sydney: Vaughn? Vaughn: How come you never call me Michael? Sydney: I call you Michael sometimes. [beat] Sydney: Vaughn.
Pretty Guardian Sailor Moon has Ami starting out calling Usagi by her surname. An entire episode is devoted to getting her to use "Usagi-chan" and "Rei-chan", and we later find out that her mother, a doctor, is only able to communicate with Ami via messages on a whiteboard.
Likewise, in Genseishin Justiriser, Yuka eventually graduates from saying "Date-kun" to the honorific-free "Shouta". Shouta, however, is a bit slow on the uptake, but Shinya pays attention and remarks on it.
On Criminal Minds, all but one of the main characters are typically referred to by their last names. Prentiss, Morgan, Rossi, and Garcia have been referred to by their first names more frequently in later seasons, but last names are still the most common.
In one of his first episodes, Rossi tells his teammates to call him Dave. Hotch at least seems to do this consistently. Likewise, Rossi tends to call Hotch by his first name.
And while JJ is the only character not referred to by her last name, it's short for Jennifer Jareau, so they're not just using her first name either.
It should be noted that when talking with each other, Morgan and Garcia don't really use either given name, preferring intimate nicknames. One episode has an emotional moment between them where he calls her Penelope.
J.J. also rarely calls Reid by his last name; she is the only one to call him "Spence".
The only character to go completely by first name is Elle Greenaway, who disappeared early in the second season anyway.
Since she's their boss, everyone also refers to Chief Strauss as "Strauss." The only one who uses her first name with any frequency is Rossi. She refers to him by his first name as well. She also calls Hotch by his first name.
On Top Gear, presenter Richard Hammond is always "Hammond" to his co-presenter James May, but Jeremy Clarkson is "Jeremy" or even "Jezza" (unless May is annoyed with him, in which case it's "CLARKSON!") On the other hand, Clarkson and Hammond are on a first-name basis with each other and with May.
They all refer to each other with their last names fairly often, especially when communicating over the phone/radio on a large challenge or race e.g.: "May!" "Clarkson!" "Where are you and Hamster?" "We're just entering Switzerland, what about you?" as mentioned in the Real Life section, this is quite common between male friends in Britain where the surname almost becomes a nickname of sorts.
Castle and Beckett. Initially, she only called him Rick when she was teasing him, but in Season 3, she occasionally used his first name in serious situations. He's called her Kate a handful of times, all of them dramatic: once when when she was emotionally upset and he was trying to stop her leaving the station, continuously shouting it out frantically when he was trying to find her in her exploded apartment, and several times in the season three finale episode.
It's revealed in one episode that he made up his last name, as it sounds better for a writer, and had his middle name legally changed to Edgar (after Edgar Allan Poe). His real name is Richard Alexander Rodgers.
Despite hooking up in Season 5, they still call each other Castle and Beckett. Even at home. In bed.
In TJ Hooker, everybody calls him 'Hooker'. Even his ex-wife. His given name, Thomas, was only mentioned once in the entire run of the series, and never again after that.
In Psych everybody calls Burton Guster "Gus." Also Lassiter is on a last name basis with everyone.
Shawn never refers to Lassiter anything other than "Lassie". Lassiter, while initially annoyed, eventually accepted it as an inevitability, or is just ignoring it, hoping the annoying creature claiming to be psychic will go away.
Gus's uncle Burton (for whom he was named) resents Gus prefering his nickname to his first name.
On The O.C., Summer persists in calling Seth by his last name, Cohen, even after they're in a relationship.
In Skins, James Cook's first name is used so rarely that it wouldn't be surprising if most of the main characters don't even know it.
It isn't clear whether or not this applies to Leverage's Parker. Also, Alec Hardison and Jim Sterling are almost never referred to by their first names.
Inverted with Elliot Spencer. His last name is barely mentioned.
On Are You Being Served?, the staff of Grace Brothers - apart from very rare occasions - always addressed one another formally ("Mr. Lucas", "Mr. Humphries", "Miss Brahms", etc.). Among the characters, Captain Peacock and Mr. Grainger tended to use each other's given names (Stephen and Ernest, respectively) most frequently in private conversation.
In the episode "The Old Order Changes", the culture of the store was (temporarily) changed to be more informal, and staff were required to address each other by first name. Mr. Lucas was not happy to have to reveal that his first name was "Dick".
On Wings, Roy usually refers to everyone using their last names. (Unless he's trying to suck up to them for some reason.)
The only person who consistently referred to him as "Bobby" was a recurring villain, who kept trying to prove that they're Not So Different.
On Auf Wiedersehen, Pet, Moxey's first name (Albert) is only used twice in the show, and the first time wasn't until the end of the second series. Sometime between these two uses, one character claimed that Moxey was his full name, although the police call him "Albert Moxey" only an episode or two later.
Maxwell Sheffield, being British, refers to Fran as "Miss Fine" even as they start dating.
He called her "Miss Fine" once or twice even after they were married.
Douglas Fargo of Eureka is almost universally referred to as "Fargo". The only people who ever call him any derivative of "Douglas" are Claudia from Warehouse 13 (who does it in response to his claim that "everybody calls me Fargo") and himself (one of his passwords is "Dougie the Vampire Slayer").
His new girlfriend (played by Felicia Day) refers to him as "Douglas" as well.
Allison used to refer to Carter by his last name. Then they became close friends and, eventually, lovers. Naturally, she switched to "Jack".
Prison Break: Varies depending on the character and their relationship. For example, Mahone calls Michael Scofield in season two when he's chasing him, varies it in season three (when they're uneasy allies), and Michael in season four when they become friendly.
Primeval: Very few people call Nick Cutter, James Lester, and Capt.Tom Ryan by their first name, and Capt.Becker's name isn't even mentioned in the series. Word of God says it's Hilary. No wonder he never mentioned it.
In The Beiderbecke Trilogy, the main characters are most commonly refered to as Mr Chaplain and Mrs Swinburne. In the second serial, the latter is utterly surprised that the former calls her "Jill", and he admits that he only did so because "I'm shit scared." This comes after the two have been in a sexual relationship for over two years, and known each other far longer.
Famously, Inspector Morse's full name Endeavour wasn't revealed until 1997.
On The Inspector Lynley Mysteries, the titular Inspector Lynley calls his partner Sergeant Havers one of two things: "Sergeant" or "Havers." He does call her "Barbara" when she visits his family in Cornwall, but when they get tangled up in a mystery - as they inevitably do - and they're back on duty, well, to quote Barbara, "It's bye-bye 'Barbara' and hello 'Havers'!" He also calls her Barbara during particularly intense or emotional moments, beginning in their second episode together ("Well Schooled in Murder") when her father dies and continuing in this vein through the next several series. By the sixth series, however, after he leaned on her after his wife's death, he calls her 'Barbara' almost exclusively, reverting to 'Havers' only when he is cross with her; this signals a fundamental shift in their relationship. In contrast to her partner, Barbara never calls him anything other than 'sir', as he's her superior officer (and a Lord to boot, while she is working-class). Still, the way she says it evolves, from stiffly formal to fond and often teasing.
Handled interestingly on Gilligan's Island. The Howells are always refered to by the other regular characters as "Mr. Howell" and "Mrs. Howell", but are on a first-name basis with each other (though "Lovey" is a pet name, not her actual given name, which is Eunice). Ginger Grant is mostly called "Ginger", but is sometimes called "Miss Grant", especially by Mr. Howell. Mary Ann, though, is almost always just called "Mary Ann" to the extent that many fans wouldn't know the character's last name (it's Summers). The Professor and the Skipper have names, but even fewer fans know them, as they're always just referred to by their titles (their names are Roy Hinkley and Jonas Grumby, respectively). Gilligan himself is the really odd case, as he is never called any other name. It's not even known if that's his given name or his surname.
On Boy Meets World, Mr. Feeny referred to all of his students by their formal title and last name ("Mr. Matthews", "Mr. Hunter", "Ms. Lawrence"), though occasionally he would use their first name instead (particularly Eric, who for much of the show's run was no longer a student of his - and presumably to avoid the problem of having two "Mr. Matthews"es). (Stuart) Minkus was the only character whom everyone addressed on a Last Name Basis, except for Topanga.
Mitchell of Being Human takes until season two to let on to the viewer that this is actually his surname (his given name is John). Justified, as being a century-old vampire he's of a generation where last name basis would have been prevalent.
Homeland. Sergeant Nicholas Brody is called "Brody" by everyone, including his wife.
On Highlander, Tessa was the only one to ever call Duncan by his first name. Everyone else ether called him Macleod or the shortened form, Mac. Even Tessa used it some of the time.
Due South Fraser-rarely did anyone ever call him Benton. Thatcher and Welsh as well, but it was usually a formality, 'Inspector Thatcher' and 'Lt.Welsh'.
Forever Knight (Don) Schanke. And by the same token, Schanke would sometimes just call Nick 'Knight'. The captains got it a lot too when they were referred to...even when the formal 'Captain' wasn't used, as in talking to them, it was often 'Stonetree' 'Cohen' 'Reese'. Lacroix was another last name guy. No one ever called him Lucian. Tracy usually only got the formal Detective Vetter version on the job sometimes, but never from Nick.
Roswell Sheriff Valenti, often even after he wasn't sheriff anymore, he was still Valenti. (Mostly because he was an adult character in a cast largely composed of teenagers; Maria's mother, his sometime-love interest, called him "Jim".)
John Steed and Emma Peel always addressed each other as "Steed" and "Mrs. Peel" on The Avengers.
On Farscape, everyone calls John Crichton just plain "Crichton." Even his girlfriend, except for a few very serious situations. The only people who regularly call him "John" are Scorpius and Maldis.
Sherlock: Is that why you're here? You're incognito? Undercover with that ridiculous alias, "Greg!" [beat] John: That's his name. Sherlock: ...is it? Lestrade: Yes! If you'd ever bothered to find out!
Mrs. Hudson is also always referred to simply as "Mrs. Hudson." One commenter described the look on Sherlock's face during the exchange with Lestrade as "The moment Sherlock began to consider that Mrs. Hudson's first name might not be 'Mrs.'"
On Dawson's Creek, Pacey usually calls his girlfriends by their last names. Namely (Andie) McPhee and (Joey) Potter.
Once Upon a Time: Rumplestiltskin's human Storybrooke counterpart Mr. Gold is regularly referred to just as 'Gold,' particularly later in the first season and especially by Regina (The Evil Queen). Though he might not even have a first name, since Mr. Gold isn't who he actually is anyway.
Person of Interest: Reese, with Finch (who only calls him "John" when Finch is worried about him and/or Reese is in more danger than usual. Although since Reese and Finch aren't their real last names (Which have not been revealed), it's more like Assumed Last Name Basis.
On Becker, the title character (Dr. John Becker) is on a last name basis with nearly the entire cast with everyone except for his nurse, Margaret and Black Best Friend Jake.
On Breaking Bad, Jesse never really gets over his high school habit of calling Walt "Mr. White." He calls his partner by his first name exactly once during the series, and it's a deliberate sign of disrespect. Oddly enough, Walt is one of the few people to consistently call him "Jesse" rather than "Pinkman."
In 15 seasons of ER, you could probably count on one hand the number of times John Carter was called by his first name. By the ER staff, anyway—his parents and his wife, did call him "John".
Rizzoli & Isles: Played straight with (Vince) Korsak and (Barry) Frost. Mostly played straight with Maura Isles, who most people refer to as Dr. Isles, except Jane who calls her Maura. Mostly averted with Jane and Frankie, probably because they are siblings who work together, and a "Detective Rizzoli" and an "Officer Rizzoli" in the same place would get confusing.
Falling Skies has John Pope, whom everyone refers to as simply "Pope." Pope himself refers to Tom Mason by his last name, at least when he's in a (relatively) friendly mood.
Most of the agents on Agents Of SHIELD are referred to by their last names: Coulson, May, Ward, Fitz, and Simmons. Only exception is Skye, probably because we don't even know her last name.
On The Big Bang Theory, Howard and Raj are often referred to by their last names (Wolowitz and Koothrappali), especially in the early seasons.