A character will perform an action and say the onomatopoeia for that action while doing so, or alternately say the onomatopoeia in place of said action.
Often done to make a character seem cuter. Can sometimes make said character annoying. Also sometimes used sarcastically, especially with sound effects like "yawn" or "clap".
There are many words that are commonly used this way. For example:
And in the OVA, Patty gets annoyed (more like in despair) that Minami's dog's paw pads don't go "puni puni".
Akira also gets in on it, whether she's being cutesy (episode 2) or not (episode 21).
Konata may enjoy doing this, but it would seem she doesn't always appreciate when people reciprocate. In one episode, Kagami lends Konata a book, trying to spark her interest in something other than manga. She then proceeds to watch Konata as she reads, all the while going "Staaaarrrrrrrreeeeeee." in the English dub, and "Jiiiiiiiiiiiiiiiiiiiiiii" in the original Japanese.
The Hamsters from Hamtaro say "Hiff Hiff" when sniffing something and "Badabadabada" when running.
They have a lot more sound effects than that. Pretty much every sound effect is said out loud.
One of the easiest ways to tell when Tsunetsuki has entered the scene, assuming you don't see her peeking out of somewhere, is if you hear a low and constant "jiiiii" sound, which is the Japanese onomatopoeia for staring (as mentioned above).
Permeates Sayonara, Zetsubou-Sensei. The voices that do it don't seem to have anything to do with the rest of the characters (it's not like a character is actually saying them), and they seem rather bored with it all.
In an episode of One Piece, Kaku narrated his own incredulous Jaw Drop. The appropriate Japanese sound effect is something like "gabiin".
Also the security camera snails of Enies Lobby, staring with 'jii—'.
During the trip to Okinawa, Tomo says "Boom, boom!" ("Clap, clap!" in the sub; "Ban, ban!" in the original) in front the main hall of Shurijo Castle as a show of appreciation.
In "Pool, Pool, Pool!", when teasing Yomi about being (supposedly) fat, she says "'Jiggle jiggle!' Hey, you made a jiggling noise!"
It doesn't come across in the dub, but in the sub, when Tomo smells sataa andagi, she says "Sniff, sniff, sniff" etc.; the original Japanese has her saying "Kun, kun, kun, kun" etc..
Fai from Tsubasa does this often - he can't whistle, so he just says "Hyuu" all the time. It annoys the heck out of Kurogane. Ironically, he can actually whistle.
Rika Furude from Higurashi No Naku Koro Ni says "pachi pachi", which is Japanese for "clap clap". She does something similar when talking about kitties. However, her most famous demonstration of this trope is her Catch Phrase "Nii-pah~!"
.hack Sora does this whenever he does something dramatic, like jumping off a tall structure ("Boing!"). Whether he's doing this to whittle down people's nerves or if he's just being the 12-year-old boy that he is is unclear.
In episode 13 of Axis Powers Hetalia, Russia punctuates his staring at Japan by cheerfully intoning "Jiii!". Three times in a row. Also, Italy is fond of waving white flags and saying, "pata pata pata pata!" which is a flapping noise, as well as squishing kitties' paws and going, "puni puni puni puni," which is a squishy noise.
In the English dub, France smacks Austria on the head repeatedly while saying "smack smack smack smack."
In one of Slayers Evolution-Rs filler episodes, Pokota gets a dramatic "death scene" after being run over by a cart. His last words: "My casting was... too late. Gurk." The fact that he pronounces the last word as "gaaku" only makes it better.
A few times in Rosario + Vampire, Mizore will say 'jiii' when staring at Tsukune from one of her many hiding places (or in plain view of everyone, like when she joins the core True Companions). Amusingly, her mother does the same thing in her introduction.
Kururu of Keroro Gunsou says "Pochi!" (meaning *push*) whenever he presses a button.
In The Melancholy of Haruhi SuzumiyaTsuruya says "nyoro", which is one of the Japanese words for "tilde" or "~". In informal written Japanese the tilde can be used as an extension of a syllable, giving it a drawn out, sing-song or playful pronunciation. This Verbal Tic of hers reached memetic status and even spawned a spinoff, Nyoron Churuya San.
Done a lot in Excel Saga. It is pretty common to see characters shouting "Gasp!" or "Shocked!".
Since Ikaros from Heavens Lost Property was short-changed in the emotional department, it's very difficult to smile. When Tomoki tries to teach her how to do so, she says 'Niyabi' with a perfectly straight face. Hilarity ensues.
An episode of Seitokai Yakuindomo has Shino, Aria, and Suzu do this simultaneously to Tsuda as he tries to write an essay for the school paper. He is understandably annoyed.
Kotetsu Kaburagi from Tiger & Bunny has no shame in speaking in onomatopoeia on public radio. And he's a single father in his thirties.
Kotetsu: ... And I went flying, like WHOOSH!, and then I was all BOOM and BANG!
To emphasize his quirky manga genius ways, Eiji Niizuma of Bakuman。 does this while working.
In Hidamari Sketch x SP episode 2, somebody is saying several of the sound effects.
In The DCU there's a particularly creepy gun-toting villain named Onomatopoeia who actually speaks in nothing but those noises, aside from saying his own name once. Obviously, the last word you would ever want to hear coming from his mouth is "Blam," as some of his victims found out the hard way. Probably the only time this trope is used dead seriously. And he does this no matter the situation; even after using the bathroom, he says "Flussssh."
The Jaime Reyes version of Blue Beetle does this sometimes. Notable in a story from a DC holiday special about a family of crooks where the first crook is punched out by Dan Garrett (the first Blue Beetle) and the second punched out by Ted Kord, each with the appropriate comic book sound effect. When it gets to Jaime Reyes (the third Blue Beetle) and he punches out his crook, he actually says the sound effect.
Hellboy does this in the comics from time to time, usually when he gets a bit too carried away beating up some monster.
Misfire: See that guy over there with the scowl and the head wound? Don't be fooled, Crankcase is actually the most cheerful person you'll ever meet. The thing is, if he smiles his precarious cranial architecture will collapse and he'll die. He's the only Decepticon who can be killed by a single punchline.
Misfire: No, not really... You're just miserable, aren't you Crankcase?
Fulcrum: Did he just say-?
Misfire: I know. You've seen it written down but never heard it said out loud, right?
Mr. Krabbs: "You've got to keep a sharp eye out for paying customers!"
In the 2011 The Muppets movie, the villain of the piece never actually laughs maniacally. He instead says "Maniacal laugh. Maniacal laugh. Maniacal laugh." in a rather flat sinister tone. Like pretty much everything else in the movie, this gets a lampshade hung on it at some point.
In FFVII: Advent Children Complete, during the extended highway chase, when Reno and Rude have their Big Damn Gunship moment, Loz decides to fight back, by lifting his motorcycle and mounting one foot on his buddy's so that his front-facing machine guns are in the air, and starts whaling on the attacking chopper, all while shouting: "Ba- Bang! Babababababang Bang BANG!"
In Heat, one of Hanna's detectives uses, "Bang, bang, bang-bang-bang," when describing the shooting of the guards at the armored car heist scene.
Gaspode the talking dog from Discworld says "bark," "whine", "woof", and "growl" instead of actually doing so.
It could have been worse, squire. I could have said "meow".
A variation is found in The Phantom Tollbooth. Milo wants to get into the Soundkeeper's fortress. Since sound doesn't exist in the Valley of Sound at the moment, he must write "knock knock" on a slip of paper and tuck it under the door. Of course, since sound DOES exist within the fortress, the Soundkeeper would've heard it even if he didn't, but it's still a cute gag.
One of the short mysteries in the Clue book series opens with Professor Plum doing this while tinkering about with what he thinks is his intelligence multiplier (it's not, actually).
In a flashback from Ghost Story, teenage Harry uses "Ka-bang!" as the verbal invocation of a force-effect spell that lets him simulate firing a gun. Lampshaded by adult Harry, who admits his choice of verbal spell-components had been even lamer when he was that age.
Live Action TV
In Living Color!: "Oh my, we seem to be fresh out of business cards. Hold on... lemme check..."
Willow:* makes indistinct movement while wearing thick fur coat*
Xander: What was that?
Willow: I shrugged.
Xander: Next time you should probably say "shrug." * leaves*
Willow does this quite a bit. In the next episode she said "gulp" and in the one after that, it was "grr"
Xander, upon seeing the insane contraption of a tower that will claim Buffy's life: "Shpedoinkle!"
Xander, brushed off by a distracted Buffy when he tries asking her out, stands there and lets out a long descending whistle and a crash noise, mimicking the sound of Wile E. Coyote falling off a cliff.
One bit on Late Night With Conan O'Brien on the Academy Awards nominations showed a clip from Spider-Man (which was up for Best Sound Effects Editing) with all the sounds clearly being vocalized by some guy, ending with him actually saying "Grab!" as Spidey grabs Mary Jane.
Another "Late Night" bit had a a fake Geraldo Rivera on the TV where the picture is real but the lips are moved by someone else. "Geraldo" is trying to look like a hero in the middle of a warzone in Afghanistan, and Conan is skeptical as he can't see any fighting. "Geraldo" starts to make noises like "kaboom" and "ratatat" to try to convince Conan, but Conan points out he is making those noises with his mouth. "Geraldo" replies "well... they have very primitive technology here, Conan."
Invoked on Whose Line Is It Anyway? with the game Sound Effects, which takes one of two forms. In the first, one performer reacts to sound effects made by another who stands off-stage with a microphone, and the quality varies (in the US version, there's a Running Gag of Ryan Styles' "squeaky squeaky" sound for bicycle tires). In the second, two audience members provide the sounds for the performers, and this is always played for So Bad, It's Good, as the audience members are nervous and giggly and do a poor but hilarious job.
Repeatedly on 30 Rock. 'Gasp', 'Sigh', even with non-sounds, like 'Twist!' Perhaps the most amusing one is Judge Dredd: "Gavel gavel gavel! I lost my gavel over the weekend, but it doesn't mean you can talk to me like that."
Taken to a new level when a flashback shows young Tracy wearing a Chewbacca costume (made out of used hair extensions) shouting "Perfectly Executed Chewbacca Sound!"
Damon: "That's for me to know, and you to dot dot dot."
A second season episode of The Good Wife has the Florricks attending an event on which an incomprehensible poem is performed. More than half of the words of the poem demonstrate this trope.
A regular feature of the Wayne's World sketches from Saturday Night Live was Wayne and Garth providing the “diddly-doop, diddly-doop” sound effects for a Dream Sequence.
And who can forget the famous "Schwiing" that Mike Myers described as the sound of a sword being drawn from its scabbord.
On at least two occasions, the device that makes the Big Wheel beep on The Price Is Right has malfunctioned. As a result, Bob had the audience shout "beep beep beep" as it spun.
An ad for the Food Network show The Secret Life Of... had host Jim O'Connor referring to his show as "The Secret Life Of Dot Dot Dot."
The X-Files had a few bleeped-out instances of swearing in Jose Chung's "From Outer Space" that, because of the Rashomon style, were done as this trope
Detective Manners: Well that's a dead bleepin' alien if I ever bleepin' saw one.
When The WB show Zoe Duncan Jack and Jane was renamedZoe... it was referred to in commercials and whatnot as "Zoe dot dot dot."
In one of the many Red Dwarf episodes where the ship is threatening to explode, Cat enters the room where Rimmer and Lister are talking to Holly. Referring to the Red Alert sirens audible in the background, he says:
"Hey guys, I think they're playing our tune, the Ahwooga Waltz! Anyone care to join me in a quickstep?"
In an earlier episode, the siren breaks, forcing Holly to say "Awooga, awooga, abandon ship!"
In Jim Henson's The Tale of the Bunny Picnic, the dog — who is the main villain — had a habit of doing this.
Frank Zappa's album Waka Jawaka is named after a popular guitar riff in rock music at that time.
Jack Black frequently "sings" guitar licks to fill out bridges in some Tenacious D songs ("Tribute" being only one example).
The Who originally wanted to have a cello section in their song A Quick One While He's Away...Unfortunately they didn't have the budget to actually get a cellist so, when the appropriate section of the song came up, the band just sang the word "cello" to the tune of the music.
In "Weird Al" Yankovic's "Smells Like Nirvana", the first bridge (after the chorus) is punctuated with "burp" and "boing".
Bluebottle from The Goon Show often reads his sound effects aloud, along with his stage directions.
In the musical The Frogs, there is the Travel Song, which has the chorus narrating...how Dionysos and Xanthias walk and what they do and what they encounter. So the song has phrases like: "Walk walk trudge trudge slog slog travel travel" and "Pant pant puff puff drip drip dawdle dawdle" and my personal favorite, "Kvetch."
In the musical Into the Woods, when the Witch describes what a giant can do to an ordinary human, she says "Boom! Crunch." at the same time as the orchestra does actual sound effects for her.
Taokaka of BlazBlue uses this on occasion ("* slurp* "), but averted it at the worst possible time: the voice actor was captioned as saying"nom nom nom", but chose to make an eating sound instead. Bang Shishigami, being more, well, Japanese, does it with the Unsound Effect ("* glare* ") in addition to playing it straight ("* thud* ". Yes, he says "thud" when he loses in Story Mode.).
In Kingdom of Loathing, your character imitates certain ranged weapons while firing them, leading to combat messages like "You point at your enemy and say 'Pew pew pew!' Then you remember you have an actual gun, so you just shoot them."
In Disgaea Hour Of Darkness, in her introductory chapter Flonne provides her own sound effects... while sneaking around Laharl's castle. "Woosh! Nin nin nin nin..."
As with the television Buffy examples, the video game has Buffy, exasperated with the Scooby Gang's none-too-subtle hints that they'd like to go to the Bronze, actually say aloud, "Audible sigh..."
The "Zzt!" sound of laying down power lines in SimCity 2000 was a placeholder recorded by series creator Will Wright. The developers liked it so much that they left it in.
An unusual variation in Enchanted Scepters. The narration "A huge tidal wave roars from the south" is accompanied by the sound of an animal roaring, followed by a splash.
In Wind Waker, Salvatore tries to increase the immersion of his battleship minigame by producing the sound effects himself: "Spliiish. Spliiish. Ka-boooom!" The Japanese version had a different voice actor, but the principle is the same.
One of the defective turrets in Portal 2 being inspected can't fire bullets so he tries to fake it by saying "Uh, blam! Blam blam blam!"
A skull cut from Halo: Combat Evolved Anniversary would have replaced the sound effects with 343 Industries employees saying them out loud.
The best weapon in Dead Space 2 is a foam finger gun. When you fire the primary attack, Isaac says "BANG! BANG!". When you fire the secondary attack, Isaac says "PEWPEWPEW!" It is exactly as hilarious as you are imagining.
The weapon is called Hand Cannon and it's a Lethal Joke Weapon. It can pop limbs off in just one hit, unlimited range, and has unlimited ammo at the expense of being harder to aim with. In ""Dead Space 3" you get the Devil Horns with does the same thing but has near unlimited ammo, so when you reload Issac rocks out as a guitar riff plays.
In Toonstruck, if you talk to Bricabrac after getting the outline of your overarching quest:
Drew: Hi, Bricabrac.
Bricabrac: Who is this... Bricabrac? The name sounds familiar, but, for the life of me, I can't seem to place the face.
Drew: He's you.
Bricabrac: Who's who?
Flux: You are Bricabrac.
Bricabrac: Yes, of course I'm Bricabrac — uh-oh, did you two sillies forget who I was?
Subverted or, um, something in Homestuck with Terezi's "PCHOOOOO". John thought she "was just making a little rocket noise or something", but it turns out it's actually the code for the rocket pack.
Later played straight with Gamzee: he both inserts honks in his chat and speech, and later, after going into a Slasher Killer mode, was the first confirmation of characters using their typing quirks in speech, speaking lines either quietly or shouting.
Delaine: DON'T CORRECT ME ON MY GODDAMN— * shlunk*
Both: * look down* "Shlunk"?
Kyran: * holds up stabbed hand* Whoopsies.
Skull attempting to eavesdrop on phone conversations.
Brent: "Skull, hang up the phone!" * CLICK*
Brent: "... Did you just say 'click'?"
Dinosaur Comics did this in one strip with Rex trying to say a "?". He simply says questionmark extremely quickly. After being told that this is incredibly lame, he tries to say "$", and succeeds. Appearently "$" sounds like a dog vomiting.
Xykon: Gosh, minions, don't let any of those big scary adventurers touch my poor little gate, located to my left with significantly less guards than the rest of the room. Just a touch would destroy it. Wink, wink.
Redcloak: Sir, I hardly think that is going to accomplish anything.
Xykon: You'd be surprised.
Redcloak: Sir, you actually said the words, "wink, wink." I mean—
Strong Bad parodies this on Homestar Runner. While showcasing the pros (and cons) of shapeshifting, his shapeshifting is accompanied by him loudly blurting out, "DWAYNE!!" In Teen Girl Squad, a comic he made about four unlucky teen girls, he also tends to narrate the sound effects like "Arrow'd!" or "Punt!"
Similar case in Once upon a Time in Mexico - they ran out of 'real' gun props, decided to use fake ones with the gunshots and muzzle flash added in post-production, and Antonio Banderas messed up a take or two by going "pchoo pchoo pchoo" while he mimed firing them.
Internet phrases (such as lol, rofl, and lmao) do this because of the lack of sound between two typing parties. Add a webcam to the chat and Hilarity Ensues as you are torn between typing out that you laughed at a joke when your conversation buddy clearly sees that you merely huffed. Or didn't even crack a smile. This leads to amusing anecdotes when people who are used to being online start saying things like "burb" (brb) when going on break at work.
Or worse, people sitting behind computers in the same room chatting with each other online, typing LOL in dead silence, without so much as looking up.
Emeril Lagasse's "BAM!"
Several actors filming the Star Wars prequels had to be told not to make lightsaber noises with their mouths.
Basketball players and spectators will often say "swoosh!" after a basket is made that hits "nothing but net."
Children are prone to this, especially during imaginative play.
And sometimes, some adults are prone to this, too, when they engage in imaginative play with their children.