Emotionally Tongue-Tied

If I were to say s----something apologetic... it would reflect my feelings in the matter... accurately.

—Valentine, Mirror Mask

Talking can be hard, especially if you're speaking from the heart. Of course this tendency is often played up in fiction to the point where characters find themselves unable to even say a particularly emotionally-charged word or phrase, often an apology or declaration of love. This may because it goes against the character's self-image, or simply because they're shy in general.

Supertrope to I Uh You Too and Gibberish of Love. Compare to Cannot Spit It Out and Gagging on Your Words.

Examples of Emotionally Tongue-Tied include:

Anime and Manga

In the manga version of Ranma ½‍'‍s Shinnosuke/Ryugenzawa story arc, Ranma is hit with a severe case of this when, for once, he's trying to be nice to Akane and speak from his heart, and he's utterly frustrated that he can't say a single word.
- When Ranma really hurts Akane's feelings in the Battle Dogi arc, he tries to apologize to her and sincerely say that he thought she looked cute. He stutters on "cute" for a while, before finally just screaming it in frustration. Much to his dismay, she thinks he's lying when he finally manages to get the word out.

Film

Otto from A Fish Called Wanda has this problem with "sorry." (At least when he's not actually sorry: When he beats the living crap out of Archie after mistaking him for a burglar, he says "sorry" very easily.)
Valentine in Mirror Mask is incapable of saying "sorry", even when he's apologizing to the heroine after betraying her. In fact, he's been unable to patch up his relationship with his tower (don't ask) for some time, because they had a fight once and "Valentines never apologize." However, when it becomes a matter of life and death, he is able to overcome his pride and say sorry. When we finally meet Other Valentine, he apologizes quite freely for things like accidentally bumping into people.
- This also applies to Helena, who can't bring herself to actually apologize after being rude to her mother. It is quite notable that the "Get Well Soon" card she gives has a drawing of Valentine's tower on it.
In Charlie and the Chocolate Factory, Johnny Depp's Willy Wonka has extreme difficulty with words such as "parent", "family", "mother", or "father". But, weirdly, not "mom and dad."
Sam from Ghost can only say "ditto" instead of "I love you." Inverted in the end, when he's the one who says "I love you" to Molly when he departs to the afterlife and she replies with "ditto".
The Collector in Demon Knight tries to seduce Jeryline into giving up the Key. His attempts are hampered by his complete inability to say the word "love".

Literature

In the Discworld novel The Fifth Elephant, Angua's werewolf parents have trouble with the syllable "vet". This makes diplomacy with the Ankh-Morpork patrician Lord Vetinari very difficult.

Live Action TV

Fonzie on Happy Days and his difficulties with the words "Love," "Wrong" and "Sorry".
Sam and Diane on Cheers encounter a similar problem.
- Sam actually has no trouble saying the word "love" ... except when he means it.
Al on Married... with Children according to Peggy "has difficulty saying certain things, like "I love you", "thank you" and "look out, there's a car coming."
Maynard G. Krebs, a beatnik in The Many Loves of Dobie Gillis, cannot bring himself to say the word "job." He also reacts with a terrified yelp to the word "work".
Minor subversion: On Sports Night, Danny finds himself incapable of pronouncing the name of tennis player Yevgeny Kafelnikov and, convinced that he's suffering some kind of nervous breakdown, races to his psychologist where he actually has a breakthrough. Nevertheless, his psychologist points out that Yevgeny Kafelnikov is simply a very difficult name to say.
In Ned's Declassified School Survival Guide, Guide to: Bad Habits, Ned's bad habit was his inability to say no.
In Red Dwarf, Kryten has a similar, but opposite, problem. His programming means he readily apologises or admits fault, but leaves him incapable of calling Rimmer a sme... a smee... a smee heee...
- This was also the theme of their music video Tongue Tied.
In the Colbert Report parody of Bill O'Reilly's "We'll do it live!" outburst, Stephen's rage is triggered by having to read out the words "I'm sorry".
In Press Gang, Lynda and Spike are unable to bring themselves to say 'love' to each other and end up resorting to anagrams, declaring "I vole you".

New Media

In the Riff Trax dub of Twilight, since there were so many awkward silences in the film, the guys usually "fixed it" by saying "...Line?"

Theater

In some stage adaptations of The Hobbit, Thorin has trouble with the word Smaug. With the right actors, it leads to a Crowning Moment of Funny.

Video Games

In the Japanese version of Breath of Fire 2, a clue as to the mercenary El (Farlan in the retranslation)'s true identity is the fact that he can't say the masculine pronoun "ore" without stuttering. In a rarely-seen cutscene, it's revealed that the mercenary is actually Princess Elfarlan herself.
In a Point and Click Game Innocent Until Caught, after you are bailed out of jail by Narm (no, really, that's his name), you have and option to thank him for it. The protagonist, after a few attempts, refuses, considering that Narm is life-defyingly stupid.
Laharl in Disgaea Infinite has to be blackmailed by Etna into congratulating Flonne for becomign an Angel Trainee again. And when he does, the words barely come out of his mouth.
An extreme version of this trope is Guybrush Threepwood in The Secret of Monkey Island, where he can't talk at all to Elaine Marley, instead muttering nonsensical gibberish.

Western Animation

In the Powerpuff Girls episode "Paste Makes Waste", Buttercup can't bring herself to say "I'm sorry" to another kid she was teasing... until said kid is turned into a giant monster and goes on a rampage, and she has to say it in order to pacify him.
Foster's Home for Imaginary Friends: In "Where There's A Wilt, There's A Way", Wilt tries to watch the big basketball game, but keeps getting distracted because of his inability to say "no", and he ends up Missing the Good Stuff.
- Marge Simpson had the same chronic doormat problem when Gill wouldn't leave their house.
In SpongeBob SquarePants Squidward has so much trouble telling SpongeBob he's sorry that it causes his head to explode.

Web Original

Invoked in Legion of Net.Heroes; after a lengthy storyline in which Legionnaire Decibel Dude is framed for murder and hunted by the Legion, he shows up with the evidence to clear his name. LNH leader Ultimate Ninja attempts to apologize, but can't quite manage the word "sorry". After two or three attempts, Decibel Dude lets him off the hook.
In Dragon Ball Abridged, Vegeta attempts to recruit the heroes for a fight he can't handle on his own any more than the heroes can. "Every fiber of my being wants to puke at once when I say this, but I need your heh... I need your he-eeh-eeeeh..." Gohan responds, "You need our help?" "That, yes."
Played for Laughs by The Nostalgia Chick. She literally gags on words like "nice" and "good".