Shinryaku! Ika Musume. In the English dub and the Crunchyroll subs, Squid Girl peppers a lot of her squiddences with the word "squid".
Often found in translations of a manga or anime featuring a catgirl with the "Nya" Verbal Tic — any syllable sounding like "meow", "mew", or "myaah" gets turned into the appropriate cat noise.
Utilized amusingly in the original Japanese of Bakemonogatari. The protagonist orders a catgirl to repeat a tongue twister he recites, and her version is hopelessly-but-cutely mangled by about twenty "nya"s. The fansubs offer an interesting solution to this: The tongue twister is given as "Can you imagine an imaginary menagerie manager imagining managing an imaginary menagerie?", and her reply is "Can mew imeowgine an imeowginary meownagerie meownager imeowgining meownaging an imeowginary meownagerie?"
The Smurf Namer is The Smurfs, of course. While the reader is, of course, left to smurf the smurf from context, it is smurfed (most directly in the lesser-smurfed Johan and Peewit smurf that The Smurfs were originally smurfed off from) that the Smurfs themselves can smurf the difference between instances of "smurf" with no smurf; it is just outsiders that smurf them as identical. Smurfly, outsiders are insmurfable of pronouncing "smurf" reliably however hard they smurf.
This is even more of a tongue twister in the comic's original language, where Smurfs are known as "Schtroumpfs".
And considerably less in Spanish, where they are called Pitufos, and they use the (very regular) verb pitufar.
Incidentally, in Smurf Versus Smurf they had a civil war (which was an allegory for the Belgian language conflicts) over whether "smurf" should be used as a verb or an adjective.
In the comic, it was nevernote except one notable instance in King Smurf parodying Cambronne's Last Stand used to cover profanities (that's what Symbol Swearing is for). In countless parodies, it's used almost only for that.
In the same spirit, in most case, the Smurfs use the word "smurf" just enough to leave the sentence understandable, except for funny or plot purposes. Johan and Peewi agreed to rescue the Smurfs from a "smurf-smurfing smurf" without other clue. So they were unprepared to fight a fire-spitting dragon. In most incarnations, the smurf would rather have said "a fire-smurfing dragon".
The scene preceding the Disney Acid Sequence in Winnie the Pooh (2011). Pooh starts honeyingnote seeing everyone as honey, and they start to replace random honeysnote words with the word honey. (e.g. "I can't wait to see the honey on that Backson's honey when he falls into our honey!") Soon, practicably every honey is replaced with the honey honey, including the honeys in the honey! Honey honey honey honey honey!
Early on in The Dictator, it is stated that General Aladeen has ordered that a great number of words in the Wadiyan language be replaced with "Aladeen"...including contradictory words like "positive/negative" which causes a great deal of confusion (as shown by a doctor informing a patient that he's "HIV-Aladeen" and the latter not knowing how to react). Used as a Running Gag throughout the film (a Wadyian restaurant has an "Open/Closed" sign reading "Come in, we're Aladeen/Sorry, we're Aladeen" and in a credits scene, Aladeen himself accidentally shoots a man in the leg because the safety catch was on "Aladeen" instead of "Aladeen").
Eric — Eric's parrot, who constantly substitutes the catchall metasyntactic variable "wossname" for random words.
In the seventh Captain Underpants book, A group of skateboarders are "duded" that Melvin duded their dudeboards. One of them says "I'm gonna dude that dude if it's the last dude I dude!"
In the Beavis And Butthead tie in book "Chicken Soup for the Butt", a section on past lives gives us this gem.
Beavis: Yeah, yeah, I remember in my past I watched a lot of those saturday morning cartoons. So like, in my past life I was a smurf. They called me "Beavis Smurf". I was hanging out with all these blue dudes. There was like a hundred of us...and one remote control. I never got to smurf the TV, because the other dudes were always like, "Wait your turn, smurfknocker." One time this one dude, "Butt Smurf," was like, smurfing with the remote control, and I was like, "Hey man, how's about letting another smurf smurf that smurf." But that smurfmunch just kept on smurfing! That was smurfy! Um, I mean, that sucked.
Pointed out, and played with a little, in an episode of My Boys, the TBS sitcom.
Scrubs: J.D. gets some Smurftacular advice from Turk on leadership:
Turk: ... Leadership boils down to three things: Smurferation, Smurfiration, Smurf. J.D.: Preparation, Inspiration, and Fear? Turk: You know it.
Henrietta Pussycat, of Mister Rogers' Neighborhood, replaced words with "meow". An interesting example because most smurfing involves replaces nouns, verbs and occasionally adjectives which can be easily guessed from context, but Henrietta would replace words at random, leading to very odd and often unintelligible speech patterns.
When he started, it was actually reversed: Henrietta would meow entire sentences except for maybe one relevant word, if you're lucky. Which is Fridge Brilliance, when you think about it: Henrietta used fewer meows as she grew up.
Lampshaded by Lore Sjöberg in The Book Of Ratings: "A middle-aged man with a hand-puppet going 'Meow meow love meow meow meow friends' in the Neighborhood of Make-Believe: beloved children's icon. A middle-aged man with a hand-puppet going 'Meow meow love meow meow meow friends' at the bus stop: a good reason to give undivided attention to your crossword puzzle."
Senor Chang on Community substituting Chang for other words. It actually catches on so much even Jeff mistakenly uses Chang a few times.
Chang: How about Chang the subject!
Ditto for Dean Pelton ("The Hunger Deans", "Don't Dean this", etc.)
Parliament's "One Nation Under a Groove" has the lines "Do you promise to funk, the whole funk, nothin' but the funk?", "Getting down just for the funk of it" and "Give you more of what you're funkin' for".
Something Awful's "wom" emoticon originated as one of these, when one poster used the nonsense word "wom" and others began using it to wom any wom in the wom. "Four score and seven years wom our fathers brought forth on this wom..."
Twilight haters often enjoy chagrinning the word "chagrin" into every chagrinning sentence they chagrin.
Nodwick has "KRUTZ!" Possibly the only smurfing word to ever have a city named after it. "Krutz" is a general, all-purpose curse word that was heavily promoted by a villain, because every time it was used, he would collect the negative energy released when someone swore.
The Killotrons in Skin Horse destroy the smurf destroy at random instead of other verbs.
Killotron-1: Happily, we are purged of our old destructive impulses and live only to destroy. And by "destroy" I of course mean "serve obediently without destroying". Unity: Nice save.
Feferi from Homestuck sometimes uses "glub" in this way.
Also, the salamanders. One in the beginning of Act 4 flash parodies it:
"GLUB!!! That's my way of saying go over there and check it out. 'GLUB' can mean basically anything I want it to mean. It's really cool having a bullshit language."
Derp and herp can be used as several part of speech. In fact you can make a sentence using only derp (and any derivatives) and a few articles: Derp derpily derped the derpy derp. And that derpy derp said "Derp." Herp can be used in the same fashion, however this troper has not seen as many examples of this as "derp"
In Educomix, Drug Abuse's adoptive mother Domestic can apparently only say the word "Word."
Twilight: Not everything has to have the word "pony" on it! Pinkie: Whatever you say, Pony Sparkle! Applejack: Top o' the mornin' to you, Pony Pie! How ya doin'? Pinkie: Oh yeah, I'm alright. Thanks for asking, Ponyjack! Applejack: Pony pony? Pinkie: Pony pony pony! Twilight: You can stop now.
Again, The Smurfs, although the animation was toned down compared to the comics. Primarily they used the word Smurf as a positive adjective.
"Hey, you have a good time last night?" "Smurf-tacular." "Yeah, I saw you leave with Smurfette." "Oh man. As soon as we got out of the bar, she started smurfin' me." "Shut the smurf up!" "Yeah!" "Right in the smurfin' parking lot?" "Smurf yeah!" "Ah, that is freakin' smurf." "You smurfed it." "That is freakin' smurf."
Then there's the South Park episode "Starvin Marvin in Space", where they meet the Marklars, who replace every Marklar, with Marklar.
Kyle: Wait. Wait. I think I can explain this whole thing. Marklar, these marklars want to change your marklar. They don't want Marklar or any of these marklars to live here because it's bad for their marklar. They use Marklar to try and force marklars to believe they're marklar. If you let them stay here, they will build marklars and marklars. They will take all your marklars and replace them with Marklar. These marklar have no good marklar to live on Marklar, so they must come here to Marklar. Please, let these marklars stay where they can grow and prosper without any marklars, marklars, eh or marklars.
The Yummies of Maryoku Yummy stick "yum" into words on occasion (i.e. "yumzillion", "yumtastic", "Yumtober the 10th", "Yum's the word").
An episode of Robot Chicken included a war between the Smurfs and The Snorks, caused by the Smurfs dumping raw sewage into the Snorks' water, who retaliate by stopping up the sewer. Papa Smurf's toilet overflows, prompting him to yell out "Oh, smurf me up the smurf!"
The Tick: In "The Tick vs. The Big Nothing", Arthur and The Tick encounter two alien races, the Heys and the Whats, who of course only say "Hey" and "What", respectively. At one point, Arthur is mistaken for a Hey and interrogated by a What who can speak Hey. He manages, in spite of having no first-hand knowledge of the language:
The watch-dog on The Simpsons who barks entire advertisements. "And now, a message from the Latter-day Saints..."
Speaking of the Simpsons, "We're on the Road to D'ohwhere" could be claimed for this trope. It has Homer hallucinating Bart everywhere, including a sign "Burt Bacharach" which turns into "Bart Bartabart".
Ugly Americans features the Bird Men, who learned to speak from a foul-mouthed tourist who brought the first pair to the States. Most of their vocabulary consists of various intonations of the phrase "Suck my balls".
Lumpy Space Princess from Adventure Time always uses the word "lump" in place of curse words. Finn and Jake use the word "math" in a similar fashion.
The Archer episode "Once Bitten" has a running gag involving the leader of Turkmenistan replacing a number of words with the name of his dog, Gerpgork. This leads to a scene where Ray and Cyril have to explain that Archer's been bitten by a "gerpgork" to some tribesmen, and get offered everything from a piece of bread to a calendar.
Non-native speakers of a language often cannot tell the difference between words that native speakers swear are pronounced totally differently. Apparently, if you never had to distinguish between two phonemes during the first few years of your life, it takes lots of practice ever to learn to notice the difference. Most well known is the "flied lice" phenomenon (or, conversely, westerners' trouble with "getting" word tones), but can also happen between more closely related language. For example, Danes commonly have trouble telling the English words "dock", "duck", "dug", and "dog" apart. Or, for that matter, Dutch people and "bat", "bad", "bed" and "bet".
Depending on the speaker's accent, those can be tricky distinctions for native English speakers. Some other examples of accent-induced confusion include "cot" and "caught", "pin" and "pen", and "Mary/merry/marry".
This is especially true of visual languages like American Sign Language. Shape, position, and especially context are important to the meaning, so it can get confusing quickly if you don't know all the rules of the language.
This can also happen for people who lip-read. Two words can look identical in terms of lip movement but sound very different, so if you don't have audio to go on, context is essential to figuring out what was said.
There are even the equivalent of Smurfs (meaning the people) for lip-readers: certain people have a natural habit in which all of their vowels and most of the consonants are produced using identical lip positions and mouth movements. (This can be also deliberately done; it's a similar technique to ventriloquism and quite a bit easier.)
This is the believed origin of the word "barbarian". The ancient Greeks thought all non-Greeks' language just sounded like "bar-bar", and therefore gave them a name to reflect that.