The other three Rangers have busted into the Queen's Asteroid Palace (which they've done before) to rescue their captain. Around the corner comes a Slaverlord, a high-end class of Mook they've shot down dozens of times before...Guns up, they're about to open fire. The Slaverlord's form then takes on Zach's form and they realize they didn't get there in time.
Another good one was in "Aces and Apes." The Rangers are chasing Lazarus Slade, who is a marginally competent member of their Rogues Gallery...but then they see that Slade has a partner. Said partner is The Scarecrow, arguably their nastiest opponent.
The last episode in season 1 of American Dragon: Jake Long. The entire huntsclan makes this face when huntsgirl uses magic skulls to wish that every member of the clan would die.
In the Road Hog episode of Angry Kid, AK decides to annoy a truck driver for the whole day by purposefully cycling in front him. However, when the truck breaks down, AK laughs before realising that hes in the middle of nowhere.
In "The Big Candy Store", Mr. Flaxseed has one before the Fighting Irish beat him to a pulp.
In "Bumbie's Mom", after Slappy Squirrel has cheered Skippy up from the trauma of Bumbie, on the plane ride home they watch the in-flight movie, which turns out to be Old Yellow. Slappy gives the "Oh Crap!" face when we hear the titular dog being shot, leading to a Here We Go Again! ending (with Slappy flatly commenting "Uh-oh.")
Buddy gives a great "Oh crap!" face in "The Warners' 65th Anniversary Special" when he is about to give a speech on the very podium he placed a Time Bomb into (to blow up the Warner siblings after they defamed him back in the 1930s), just as the bomb's alarm clock starts ringing...
Ozai gets a somewhat more subdued Oh Crap expression earlier in the same fight, when Aang catches his massive Comet-enhanced lightning attack and looks like he's going to redirect it right at Ozai, who unlike Aang had no way to defend against lightning. But since Aang refused to kill, he redirected the lightning into the sky instead. Something in Ozai's smirk immediately afterwards gives the impression that he had expected that but he still doesn't try using lightning again.
Jet gets a slow-motion zoom-in shot of this nature when Long Feng kills him.
This is Aang's reaction when he just barely manages to save himself from getting skewered with a throwing star in his first battle with Mai.
Sokka also gets several, one notable example of which is his expression in Episode 2, when the Fire Nation boat is about to mow him down.
The look on Zuko's face when he realizes that his sister is about to wipe the floor with him at the start of Book 2 really says it all.
Also in the Book 1 episode "The Storm". During a flashback, younger Zuko does this when he realizes that his own father is about to burn the royal crap out of him.
Actually, Zuko gets a lot of these... practically once an episode during Book 1.
One particularly epic one came in chapter 18 when Zhao sees and recognizes the swords used by the Blue Spirit (Zuko) when he freed Aang from the Fire Nation fortress. Zuko instantly realizes that Zhao just put two and two together and the look on his face just screams this trope.
In "The Day of Black Sun", we get a close-up of Aang's face panning out to reveal an equally shocked Sokka. Not to mention a triple example from Aang, Sokka and Toph◊.
The characters and viewers get one towards the end of that two-parter with the reveal not only that the mechanist's air balloon had been mass-produced by the Fire Nation, but that they'd gone and invented airships.
Zhao when La grabs him. That is all.
A little bit before then, Zhao realizes he's in deep shit when he kills Tui, and Iroh retaliates.
Azula herself gets one in the Grand Finale... when Katara encases her in a block of ice.
Katara gets one of these towards the end of Season 2, when she discovers Zuko in Ba Sing Se, goes to the palace to report him, and there runs into Azula and company disguised as the Kyoshi Warriors. Not your lucky day, Katara.
After taking down a bunch of Fire Navy ships at the North Pole, Aang looks out a bit farther to sea and realizes he still has a few hundred left to go...
Crowning one goes to the opening of season 2, where Azula and her elite guard almost tricked Zuko and Iroh onto the Fire Nation boat. When the captain uttered "we're taking the prisoners home", not only does he get an Oh Crap face, but so do Azula, Iroh, and Zuko. Four for the price of one! Though Iroh's face was more of a "Time to kick ass" face, as he suspected this kind of treachery, and Azula's was more of a "you idiot!" face, as she was looking directly at the captain.
In Iroh's short in "The Tales of Ba Sing Se", he happens upon some kids playing earthbending ball who then break a window. He tries to tell the kids that they should own up to it when a huge guy says (paraphrasing), "The window won't be the only thing that's broken" and Iroh tells the kids to run for it.
The Earthbender general in "The Avatar State" gets one when he realizes that Aang in the Avatar State is not too happy with him.
One more for Azula (as the show's resident Magnificent Bastard, she doesn't get too many herself), during the season two finale when Aang collapses the rock formation she's clinging to. Particularly notable as the only time we ever hear her gasp in fear.
Hama gets two moments in The Puppetmaster; once when Katara breaks free from her control, and again just before Katara floors her with a powerful waterbending attack.
From the first season, the episode that introduces Hei Bai has two, both involving Roku's dragon. The first, of course, is when Aang sees the dragon heading towards him, and realizes that he can't bend in the Spirit World, and the second is when the dragon banks up and flies towards the ceiling in Roku's temple. Seeing that the dragon never did intend to hurt him, though, each of these instances would probably count more as a subversion.
When the sandbenders steal Appa and Aang finds out, it's too late for them to do anything about it. Aang gets Glowing Eyes of Doom, and the sandbenders realize that they are facing a Physical God who is insanely ticked. Sure, Aang cools down before any real damage is done...but even Sokka and Toph were running away scared.
Oh man, when Avatar Roku manifests before the traitorous fire Temple Sages, he ain't happy about the way they've been treating his reincarnated self. The poor sages don't even stop to think, no - they just shit their pants and RUN.
D-list bad guy the Mandrill gets a great example of this during the beginning of episode 3. After robbing a bank he is confronted by...the Wasp. He's less than impressed. Then Iron Man shows up. Still confident. Then Thor, Giant-Man, and the Hulk show up. His spectacular oh crap face is followed by a wise choice to surrender.
Another great example comes when the Avengers must stop Kang from taking over New York. When Hawkeye and Hulk encounter some of Kang's robots on a bridge, Hawkeye tells the Hulk to go rest while he fights them solo. The robots then combine into one Giant Mecha, leaving Hawkeye shocked.
Five Avengers react like this after Ultron's beam apparently causes Thor to vanish.
In one Cold Opening to Batman: The Brave and the Bold, Wildcat is confused as to why he should be careful around Bane, noting how scrawny he looks. By the time he looks back, Bane's beefed up on Venom, causing the elder hero to utter "Oh, crud..."
Terrorsaur: Blast those Maximals! They destroyed my power! But at least I got rid of Megatron. Megatron: Well, well, look... who's... back! Terrorsaur:(tiny voice) Help!
In "Other Voices Part 1", Optimus Primal has been captured by the Vok and scanned (which is incredibly painful). After recovering somewhat, Optimus opens his eyes... and nearly shits himself when he sees the head of Unicron staring down at him. He calms down when the Vok explain that they looked into his memories and are using A Form You Are Comfortable With.
Happened to Butt-head in Beavis and Butt-Head's Butt-O-Ween special. But, being Butt-head, his facial expression remains static, and his reaction amounts to "Uhh, uh-oh."
In the Ben 10 episode "Ben 10,000 Returns", when young Ben as Waybig is hit by Eon's time aging ray and crumbles into a big pile of dust, Professor Paradox and Ben 10,000 both give a great open-mouthed oh crap face from a side view.
Tom in Chaotic gets a fantastic one in the episode "Battle Lessons". During the episode, Tom meets and subsequently befriends a mysterious player named Kit, who soon decides to challenge him to a battle to get Tom over the loss of his scan of Maxxor, his favorite creature, due to being forced to trade it away a few episodes prior. After getting repeatedly curb-stomped by Kit's strange creature and locations, Tom nearly goes to quit the match when Kit finally reveals who he really is.
In the episode "Seer No Evil", Monterrey Jack has one when he realizes that he, Gadget, and Dale are in a trunk, which is the last of the fortune teller's predictions that ends with Chip's death. He doesn't die after all.
This is the typical reaction by the others whenever Gadget uses the words "Should" or "No Problems" in reference to whether one of her inventions will work. A spectacular failure inevitably follows immediately after.
Chowder: In "The Party Cruise", Mung Daal offers to tell Chowder one of his fishing stories.
Mung Daal: Did I ever tell you the story of my famous one-thousand-day fishing trip? Chowder:How many days? Mung Daal: A thousand. Chowder:Oh gosh...
Mostly everyone in Code Lyoko will experience something that would result into "Oh, crap" faces. This mostly happens with XANA attacks, but rarely will it be because of something they did.
Yumi pulls this face when she realizes Jeremie's notes are as big as War and Peace.
Ulrich pulls this reaction when Jeremie tells him that the batteries on his robot died.
Dan Phantom gets one in "The Ultimate Enemy", when he's sent flying into a petrol tanker and quickly learns one of the drawbacks of having Flaming Hair, as the vehicle explodes.
In "Memory Blank", Danny himself gets one when he realizes that when Sam wished she never met him with Desiree is around to hear it.
Darkwing Duck: This reaction usually followed the mighty midnight mallard's confident heroic banter right before he got pummeled. It never lasts long; in mere seconds, he's back to scheming and scrambling for the means to thwart evil.
"Life, the Negaverse, and Everything": Darkwing has this reaction when Megavolt rallies Bushroot, Quackerjack, and the Liquidator to prove to Negaduck that they're not losers, seconds before the four villains rush the unfortunate vigilante.
"Dry Hard": Darkwing gets a quiet freaked-out reaction when he realizes that the water in the vat Fludd fell into has dissolved the stick he was trying to use to retrieve him.
On the villainous side, Sharp's face turns into an expression of shock and panic when Hammerhead discovers that he doesn't have the list of agents he claimed he would be auctioning off.
"Darkwing Dubloon": Megavolt gets this expression on his face after Darkwing magnetises him and he finally contorts his body to avoid being impaled by the flying cutlasses of his crewmates - only to see a cannon skidding across the deck toward him...
A much more serious example comes from Gosalyn verging on outright Heroic BSoD, when she first encounters the resurrected Taurus Bulba (who murdered her grandfather in the backstory to "Darkly Dawns The Duck") in "The Steerminator."
The DC Animated Universe is fond of the "Oh, no" variant, and manages to keep it consistently funny, at that.
The greatest example possibly comes in Justice League Unlimited, when the time-traveling villain Chronos sends one of the Jokerz back to the time of the dinosaurs for betraying him:
Kalibak: I just flattened Wonder Woman! You really think you can beat me? Batman:I'm not trying to beat you. I'm trying to stall you. Kalibak: Stall me? For what? (turns to see Superman behind him) Aw— (punched in the face)
At the very end of "Secret Society", we are treated to a gorilla's Oh, Crap! face after Grodd attempts to use his psychic attack on Superman, who manages to resist enough to flick Grodd in the nose, sending him flying. A little earlier, Shade had one on as Superman, in the blink of an eye, interposed between his fist and Batman.
There's a pretty priceless one early on when Lex Luthor is informed that while humans are mostly unaffected by Kryptonite, studies have shown that it can cause blood poisoning in terrestrial life if the subject is exposed for a long period of time. Lex happens to carry some around in his pocket.
Luthor tops himself in the episode "Alive!", part 1 of the series finale. His change of expression from exultant triumph to shock and horror when he resurrects Darkseid instead of Brainiac is just epic.
Luthor has another classic moment of dismay after AMAZO copies Martian Manhunter's abilities (which include telepathy) and tells Luthor, "So, you lied to me...".
At the end of the episode "This Little Piggy", when Zatanna is magically tossing things at Circe:
Circe: Insolent trickster! You dare to strike... (smacked with a chair) You dare to strike... (smacked with a table)You dare to strike...(covered in a tablecloth, yanks it off) QUIT IT! Oh, no...(hit by a piano)
In the episode "Ultimatum", Giganta gets Bizarro to distract Wonder Woman while she goes to free Grodd. On her way to his cell she runs into a tiny Long Shadow blocking her way:
A brief one from the first part of the above-mentioned Chronos episode: Green Lantern and Batman are sitting in the cafeteria discussing their respective love lives; Batman is explaining that Wonder Woman is not his girlfriend.
Batman: Diana's a remarkable woman, she's a valued friend. She's... Lantern gives him a look; Batman notices Batman:[eyes slightly wide] ...standing Right Behind Me, isn't she? Wonder Woman: Don't let that stop you... keep digging.
From the JLU episode "Grudge Match". Hawkgirl, Vixen, Black Canary and Huntress, four of the toughest women in the League, have just shrugged off the mind control forcing them to fight each other. They stand ready to face the villain... who brings out a mind-controlled Wonder Woman. Four to one odds and they're still in big trouble.
Vixen: Anyone got a plan? Hawkgirl: Yeah. Try to stay alive. Huntress: Anybody got a good plan?
This one takes most of the episode "Far From Home" to set up. Supergirl, Green Arrow, and Green Lantern are abducted to the 31th Century by Brainiac 5, who is nearly clobbered by Supergirl before he can explain that he's a good guy, unlike that OTHER Brainiac. The two eventually hit it off.
In the last scene, GA and GL are back in the present, and show Superman a farewell video from Supergirl: she's staying in the future because it's more like her lost home, and "Also, I met this boy...." It's a heartwarming moment as Superman realizes that although this is the best for her, he may never see his young cousin again.
Joker: See, Batsy, I think of everything! Hahahahahahaha— AAAAAAAAAAAAHHHHHH!
"Almost Got 'Im": Several villains have been sitting around playing poker and sharing stories about how they almost killed Batman, but failed. The Joker's story ends with him successfully capturing Catwoman and he reveals her location, and that he's about to head off and finish her. Then Killer Croc says "I don't think so" in Batman's voice, and the Joker's expression in the split second before he's thrown across the room is priceless.
Harley Quinn gets one in the same episode; guarding the Death Trap that Catwoman has been placed into when Batman comes calling, when Batman captures her Harley smugly gloats that he can either beat her up or save Catwoman, and can't do both. Unfortunately for her, she's neglected to consider the large circuit breaker the two are standing beside, and when he just shuts the power off her expression and reaction is even more priceless:
Charlie returns the favor by trapping the Joker in an alley with a bomb. Joker is absolutely terrified, thinking he's actually going to die, and cries out for Batman to save him. Batman is actually about twenty feet away, watching the whole thing, and Charlie knows it. But Batman lets the Joker sweat for a few minutes before trying to stop it... and revealing that the bomb was a fake all along (and Collins knew it).
"Fear of Victory," when a bookie's henchman is sent to find out why "Mr. Lucky" never loses, no matter how many bets he places. The henchman follows Lucky to an abandoned horse stall, threatens him, and goes to pull him out of the shadows... only to find out he has just collared the Scarecrow. Things go downhill from there.
Harvey: There's just one problem. Rupert Thorne: What's that? Harvey: You're talking to the wrong Harvey.
The scene from the episode of Static Shock where the Joker shows up to cause trouble in Static's neck of the woods. At the end he's been defeated and tries his famous joybuzzer trick on Batman, but Static grabs his hand instead. He gets an Oh Crap look he gets when not only was his joybuzzer ineffective, but Static decides to return the favor in his own way. The Joker was very shocked by that turn of events.
"Solar Power" , this is essentially Luminus' expression when he realizes that the depowered Superman is returning to normal.
Same reaction for several alien bounty hunters in "The Main Man", Superman, weakened by exposure to simulated red sunlight, tricks them into throwing him into an Earth-like habitat aboard the Preserver's ship. Cue theme music.
"Superman's Pal" gave Metallo a brief one when he realized that Jimmy Olsen had just removed his Kryptonite power source. He has time for a brief shriek before he collapses.
On Drawn Together, Xainder has these a lot, more often than not due to Captain Hero.
Played with in the episode "Electric Eggs", after the Urpneys bump into Rufus and Amberley, expecting the worst, only for the latter to perform this trope as well and run for it.
Rufus, Amberley and Albert pull a particularly epic one in "The Dream Beam Invasion", when Frizz and Nug start growing to enormous size and give them quite a nasty glare.
The season 2 finale of Duck Dodgers has rogue Martian General Z-9 abduct the Martian Queen and steal Duck Dodger's ship as he leads an armada to Earth. However, it is not Z-9 who has the Oh Crap! moment, even when he realizes that he doesn't, as he'd hoped, have the satellite defense codes.
Counselor Dish:Shall we call off the attack, General? General Z-9:Maintain course, Counselor Dish. Counselor Dish:But, no Martian ship will make it through the shields. We'll be vaporized. General Z-9:We're notina Martian ship. Duck Dodgers(On a pursuing Martian ship): WE ARE!
"Where No Duck Has Gone Before": A lot of the protagonists (and the antagonist) have their own terrified reactions as they realize that they're really in space with real aliens.
In "Hero for Hire", Launchpad visits Ma Beagle. He saw a picture of her with her children... the Beagle Boys.
"Til Nephews Do Us Part": After Millionara Vanderbucks loses Scrooge and Flintheart consoles her, he gets this when she asks if there's a "MRS. Second Richest Duck in Duckberg."
The Dungeons & Dragons cartoon usually kept with the 80s theme of nobody dying or seriously trying to kill the villain except for the episode "The Dragon's Graveyard" where the heroes, fed up with Big Bad Venger decide to finish him for good. The look on his face when he realizes he is trapped and they are out to finish him says it all.
The Earthworm Jim cartoon gave many of these moments to its villains, particularly to Psycrow, as in: "...You're gonna hit me really hard now, aren'cha?" But special mention has to go to the Oh, Crap! moment they work in to a musical number.
The characters of Ed, Edd n Eddy got three in quick succession in the last ten minutes of the Grand FinaleMovie: Eddy, when his brother demanded that he "play Uncle", Double D when Eddy's brother starts beating the shit out of Eddy, and everyone else when Eddy's brother starts to beat up Double D using Eddy as a club.
Eddy's Brother when he sees a steel door rocketing straight toward him.
Brian and Stewie in "I Dream of Jesus" when they find out the present Jesus gave Peter was a Surfin' Bird record.
Meg: What did he give you? Peter: Oh you haven't heard? Stewie:CRAAAAAAAAAAP!!! ( Or FUUUUUUCK!!! in the uncensored version)
In The Flight of Dragons, when Carolinus realizes that not ALL of the dragons have been put to sleep. Ommadon's dragon Bryagh is still active.
In The Flintstones Meet Rockula and Frankenstone, Fred goes from amused at the thought of Rockula trying to make Wilma his bride to terrified when Wilma reveals that Rockula knows that he can't marry a married woman and thus plans to make her a widow (in other words, kill Fred).
In Futurama, one of Bender's more common expressions is "I'm/We're boned!", for more or less these kinds of situations. He gets himself into trouble a lot. Another Catch Phrase of his is "Cheese it!", also for these kinds of situations.
In Gargoyles, The normally unflappable Owen gets one when Anastasia Reynard says that she's remarried her first husband. Why this is is a mystery until both their true natures have been brought to light.
In the G.I. Joe: A Real American Hero episode "The Gamesmaster", Flint has this look when, after challenging the Gamesmaster to a fight, the Gamesmaster stands up from his chair and is revealed to be over ten feet tall.
Noah's neighbors go from mocking him and planning to set the (currently occupied) ark on fire to fleeing in terror when the rain begins to fall, letting them know he was telling the truth.
When Esther asks her husband the king to save her and her people from the plot to kill them, Haman's face contorts in shock and horror as he realizes he picked the wrong nation on which to attempt genocide.
Harley Quinn (2019): The episode "A High Bar" sees the titular villainess have a moment when she crashed the Bar Mitzvah for Penguin's nephew, when after she beat up a bunch of guards and tried to break into a vault only to learn she hurt a bunch of improv actors, tried to steal fake money, and ruined the Penguin's surprise.
Hey Arnold!: The episode "Arnold Betrays Iggy" has two such moments. Arnold, who promised Iggy to not tell anyone that he wears bunny pajamas, has a moment of Stunned Silence when Sid and Stinky manage to figure it out on their own. Later, as Iggy is about to make Arnold go out in public wearing bunny pajamas for his alleged betrayal, he overhears Sid and Stinky talking about how they "kinda pulled the truth out of him" and realizes Arnold was telling the truth, just before he steps out for his humiliating walk-of-shame.
Iggy: ARNOLD, WAIT! YOU DON'T HAVE TO DO THIS!
Both main characters of Invader Zim have been on the receiving end on this trope on several occasions, the most obvious example being when Dib sees the massive water balloon about to crush the city (and him) in "The Wettening". Even secondary characters aren't immune, with the Tallests (along with their entire crew) displaying classic Oh Crap expressions as their ship, being controlled by Zim, is about to crash into a sun.
The intro to Inspector Gadget has Gadget do this right when he sees he's handcuffed himself to a lit bomb.
Ron, after inventor Cyrus Bortel informed him that the Moodulator has locked Kim in an "irreversible frenzy of rage..."So I hope she's not angry at anybody because whoof...that'd be bad." Ron had just given her the "let's just be friends" talk.
Drakken also has a Mood Whiplash "Oh, crap!" moment from gloating until when he realizes Shego must also be wearing a Moodulator like Kim, which he just locked into "an irreversible frenzy of rage":
Drakken: A scorned woman! HAHAHA! The perfect weapon! Bortel: If she's wearing Moodulator #1, then where is the second one? Drakken: The second one?... Uh-oh... Shego: DRAKKEN!!!!
When gloating about having defeated Kim, Drakken looks up◊ from his knees to see... one very pissed off Kim◊. So scared is he that he only reacts after she punches him across the room.
And Kim's not invulnerable either. She has this reaction upon meeting Oliver, the 7 foot tall by 4 foot broad boyfriend of Vivian.
Both and Kim and Shego (who was good due to the attitudinator) had this reaction when Ron was turned evil again.
Kim: Not again. Hego: What happened to him? Shego: I think he's evil now. Hego: How bad could that be? Shego:You'd be surprised.
In another episode, Kahn's mother comes to visit, and starts busybodying over Minh's meal. Connie walks in to say "hello", sees them fighting, and says "Oh no, already?" before quickly leaving.
In another episode, the insane Trip Larsen tries to commit murder-suicide with Luann by taking her through the pig slaughtering machine at his pork product factory. Luann manages to escape, but he stays on the conveyor belt, Laughing Mad and still intending to kill himself. Before he reaches the grinder, he gets an electric shock right to the head which cures his insanity... just in time for him to realize exactly what he's doing and where he's headed.
The Disney short Lambert the Sheepish Lion: A mean, hungry wolf is about to chow down on Lambert's sheep mother - until Lambert lets out a huge roar, immediately changing the look on the wolf's face.
In the second episode, Korra participates in a pro-bending tournament. Tenzin hears about this, and comes to retrieve her. Korra gets knocked off the platform during the tournament, and as she swims to the edge, Tenzin is standing not five feet from where she pulls herself up. She tries brushing it off casually, with only slight amounts of success.
In "When Extremes Meet", this is Korra's priceless reaction to Ikki revealing to Asami, Mako's girlfriend, that Korra loves Mako
In the same episode, Korra gives one when she realizes Tarrlok can bloodbend and in the next episode Tarrlok gets one when Amon resists his bloodbending.
In the season finale, Amon when Korra finally starts airbending and when it's revealed to his followers that he's a waterbender and bloodbender. These are the only two times in the series where his unflappable demeanor goes away. It's also the only time in the series where he has no plan to fix it.
Pema pulls one heck of an Oh, Crap! face when Asami and Mako start to argue.
The reveal of the Colossus to the outpost in Book 4.
In Legion of Super-Heroes, when Imperiex realises that by turning the sun yellow, Brainiac 5 effectively turns the whole population of Kandor into Supermen.
Imperiex:I suggest we worry about unshrinking ourselves WHEN THERE ISN'T AN ARMY OF SUPERMEN BEARING DOWN ON US!
That Dark Circle guy's face when he pushes the trigger for a bomb supposed to blow up a satellite but it fails to go off is classic.
Dr. Londo's pretty good at pulling these, first was when his mutated creatures turn on him and the second time has his clone display an even more accurate depiction of this trope when his attempt of reasoning with his berserk son fails who subsequently kills him.
Even Bugs Bunny had moments like this; once in a Mad Scientist Laboratory when he sees the Hyde-like monster behind him, and again when he accidentally takes off in a rocket and looks down to see the Earth falling away below him, and an epic one in Rebel Rabbit when he saw the whole US Army coming after him... And then there's What's Opera, Doc? when Elmer shows of his magic helmet's power for the first time.
Chuck Jones is clearly the undisputed master of the cartoon Oh Crap face.
You know Bugs is in serious trouble when his eyes widen and ears fall.
In a lot of cartoons with Yosemite Sam, he thinks he has gotten the better of Bugs, only to realize he's in trouble, and goes from an Evil Gloating to and Evil Laugh and then to an Oh, Crap! rather quickly. For example, in "Hare Lift" when he parachutes out of the plane with his stolen money:
Metalocalypse, "DethHealth": Nathan Explosion gets one of these in this episode. The usual mayhem goes down at a Dethklok show, with much of the debris nearly missing crushing the band:
Nathan Explosion:(with requisite expression) Oh shi— we nearly died!
The guys' reactions when Offdensen angrily confronts them about booking a gig in Syria definitely qualifies. Considering that it's the closest Offdensen has ever gotten to completely losing his composure, even some of the fans had Oh Crap reactions to it.
In the Mickey Mouse short The Pointer, when Mickey turns around and realizes that whom he thought was Pluto is actually a bear. While looking right into the bear's jaw.
Twice in "Meet Mr. Bogus" does this happen. Bogus gets one when he sees that part of the rafter that he had been skateboarding on had been gnawed away by Ratty, while Jake and Butch also get this reaction when they see the lawnmower, with Bogus on it, heading in their direction.
In "Shop Around The Clock", the white rats get this reaction in the second act when they see the dalmatian head their way, intent to fetching the dog treat that Ratty threw on top of their cage. Bogus also gets one before getting hit by a blue squeak toy that Ratty and the white rats have catapulted at him.
In the third act of "Museum Madness", Ratty gets one before Mole inadvertently knocks him off the plank of the pirate ship. He gets another one a little later afterwards when Mole also inadvertently causes the cannon to tip down while trying to fire a shot, before the shot causes the pirate ship to sink.
Bogus and Tommy both get this reaction in the first act of "Lights, Camera, Bogus", when Brattus gets eaten by the robot dinosaur.
Two examples in "Good Sport Bogus"; the Dirt Dudes both get this reaction in the first act when Bogus uses his spaceship to fire a stream of water that blasts them away, and Bogus himself gets a rather hilarious one in the third act when he sees the arrow soaring directly toward the archery target that he's stuck in.
In the first act "Computer Intruder", Bogus and Baddus both get this reaction upon discovering the huge and evil Bogus clone playing them for saps against each other.
This was Ratty and Mole's reaction near the end of the third act of the episode "Babysitting Bogus", when they realize that there's no way for them to escape the baby.
In the second act of the episode "Bookstore Bogus", Bogus gets this reaction before crashing into the bookshelf, while in mid-flight while pursuing Ratty and Mole.
Bogus gets this reaction when he realizes that he's about to get smacked by the tube of toothpaste that he just jumped over in the first act of "Bad Luck Bogus".
Blossom, Bubbles, and Buttercup are hit with this in "The Boys Are Back In Town" when they see the now-gigantic Rowdyruff Boys, and again at the end when Him tells them they may not be so lucky the next time they deal with the Boys.
Buttercup has this face when she gets busted for throwing glue at Elmer in "Paste Makes Waste".
Many times, usually by Sydney and Sean whenever Jet does something stupid or is about to expose his alien identity.
Sean screams in terror every time they blast into space.
In "Back to Bortron 7", Mindy freaks out upon realizing that the hologram of the Propulsion house has disappeared.
The Real Ghostbusters has the characters have this twice over after Cthulhu himself is summoned. First, the Ghostbusters try blasting him and cause only minimal damage, which heals up immediately anyway. When the Ghostbusters try again, Cthulhu looks directly at them.
Winston: Uh-oh! I think we made it mad! Egon: RUN FOR IT!
Megabyte from ReBoot is not only a stoic and sophisticated Chessmaster and master manipulator, but also the most physically-powerful program in Mainframe. His memories of Enzo Matrix are of a brash, overconfident, hyperactive little boy. So when the now grown up Future Badass calling himself Matrix falls for his goading, tries to beat him up personally, lands one, punches him across the room, and leaves a fist-sized dent in his chest... it's one of the best facial expressions in the series.
Later that same episode, after Matrix defeats him, and refuses to kill him, Megabyte prepares to escape Mainframe anyway by using a portal to the Supercomputer. Then Mouse hacks the portal to send him to the Web, instead. His reaction when his last gambit fails says it all.
Muscle Man has a tendency to say "Oh no, bro!" when things start to get bad.
There also a couple usage of this trope: Benson saying "We're dead" in "Dizzy" and Mordecai saying the exact same thing at the ending of "Party Pete".
Both Ren and Stimpy get one in The Ren & Stimpy Show short "Nurse Stimpy" when both characters don nurse outfits to take care of the other, Stimpy more than Ren when he realizes that Ren's doing it as revenge.
Played for raucous laughs in an episode of Rocko's Modern Life. One of his new jobs in a long string of job hunting results is him working at what is for all intents and purposes a phone sex setup (this series got a lot under the radar). Of course, when he and the person on the other line recognize one another's voices...
Rocko:(monotonic, unenthusiastic) Oh baby, oh baby, oh baby... Mrs. Bighead: ... Rocko? Rocko: ... Mrs. Bighead?! (both slam the receivers down on their respective phones)
The eponymous protagonist spends a good portion of episode 2 like this, having been flung into the dystopian future where he's falling between skyscrapers and getting hit by flying cars and nothing makes seeeeense. Poor guy.
Aku gets an absolutely hilarious one when Jack's sword doesn't harm Jack to the point that his flaming eyebrows snuff out!
The look of utter confusion and horror◊ on Jack's face when he finds his sword, a sword forged by the gods and the only thing capable of harming Aku doesn't work on the Minions of Set. He cuts one's arm off and then nearly slices it in half, but the damage heals instantly. As if they weren't already impossible to fight as is. Jack spends most of the episode looking like this.
Aku gets this expression whenever Jack gets the jump on him; for all that he's an immortal sorcerer, Jack's sword is still the one thing that can destroy him forever, and Jack is a master of it.
None exceed Aku's dawning horror in the finale, however, when Ashi opens a time portal that sends her and Jack back to the past. Except perhaps past Aku's expression when future Jack emerges mere moments after past Jack was sent away. An expression that remains on his face for the final few minutes of his existence.
Invoked numerous times on Sealab 2021, but especially notable during Quinn's Mushroom Samba episode with the seal, Stinky Pete, being chased by a shark.
Stinky Pete: Oh crap, oh crap, oh crap, oh crap, oh crap, oh crap, OH CRAP ON A CRAP CRACKER!!
Doyle does this (even going so far as to utter "Oh crud!") as he notices the time has run out on his emergency air supply in The Secret Saturdays episode "Where Lies the Engulfer".
She-Ra and the Princesses of Power: When Adora finally gives up on Catra in "The Portal" and gives her a Death Glare, Catra's resultant expression manages to convey, very efficiently, 1) that she knows full well that she's crossed a line she's not going to get back across in a hurry, 2) that she knows Adora will not be holding back next time they meet on the battlefield, and 3) that since Adora is able to shatter stone with her bare hands when in her Super Mode2) is going to hurt.
"Bart the Fink": when Krusty gets arrested for tax evasion, we see one side of a telephone conversation with his banker in the Cayman Islands.
Banker: Hoho, I'm sorry, I can't divulge information about that customer's secret illegal account. (hangs up) ... Oh crap, I shouldn't have said he was a customer. Oh crap! I shouldn't have said it was a secret. Oh crap! I certainly shouldn't have said it was illegal!... Oh, it's too hot today.
In the "Treehouse of Horror VIII" segment "The Homega Man", Comic Book Guy does this as a nuclear missile hits him dead on in the face.
Comic Book Guy: But Aquaman, you can't marry a woman without gills! You're from two different worlds! (looks up and sees missile) ... Oh, I've wasted my life.
Troy McClure gets a literal "Oh Crap" moment in "Marge in Chains" when, during an infomercial for Dr. Nick's Juice Loosener, he tries on Dr Nick's Tanning Cream/Laxative.
Bart Simpson has one of these moments in "Principal Charming" after he burns his name into forty-foot long letters on Springfield Elementary School's athletic field with grass killer. An enraged Principal Skinner roars Bart's name after seeing it, and Bart gulps both audibly and nervously. He then has another moment when Skinner is yelling at him in his office:
Skinner: Surely you realized that by writing your own name in forty-foot letters, you would be caught. Bart: Maybe it was one of the other Barts, sir. Skinner: THERE ARE NO OTHER BARTS!!! Bart: Uh oh.
Near the end of "Marge vs. the Monorail", Smug Snake Lyle Lanly loses his smug expression and freaks out when he realizes that his plane to Tahiti is making a stop at North Haverbrook, the last town he ruined with his monorail scam. His panic is justified — moments after the plane lands, an angry mob of North Haverbrook's remaining inhabitants attacks it.
In "Marge in Chains", Otto sunbathing on a rooftop, just as he realizes he's about to be hit by a dollop of vomit infected with the dreaded Osaka Flu falling from Arnie Pie's helicopter. Shown from the perspective of said dollop.
"And now a word from our new sponsor...PERCODAN?!? AW CRAP!"
Nelson in "22 Short Films About Springfield", when he realizes that the Very Tall Man has stopped his car and is coming after him for laughing about his appearance. (Then again, after Lisa tells the guy that Nelson is hiding down the manhole.)
In the segment "Citizen Kang" of "Treehouse of Horror VII", Homer has this when he realizes that he just launched Bill Clinton and Bob Dole out of the UFO tubes and into space, killing them and dooming the Earth to vote between their alien impersonators.
Homer: Oh no.
In "Bart Has Two Mommies", Homer has this reaction when he takes a bite out of a peach and remembers that he filled it with antifreeze to poison the monkey that kidnapped Bart. We don't get to see him get sick from it.
In "Child Abduction Is Not Funny", the owner of the city wok does this absolutely according to the book: He gives a big speech, realises something's wrong, sees the fuse, follows it with his eyes, says "Oh Crap" and gets blown away, together with part of his wall.
Used by Mr. Krabs in an episode when SpongeBob tries to free the captive jellyfish from him:
SpongeBob: And now I'm going to set these jellyfish free! (attempts to open the door) Mr. Krabs: *laughs* Well, you can't. The door's voice activated, and it will only open if I say "Open". (short beat, then he suddenly realizes that he just said it)
In "Friend or Foe", Plankton simply says "Oh, barnacles." when he deploys a jetpack only to see that it's upside-down, causing it to send him flying through the floorboards of the Krusty Krab.
In "Clams", Mr. Krabs has one of these when he hears ominous music following his one millionth dollar being cast out to sea:
Mr. Krabs: Oh no. SpongeBob, quick, reel it in! Can't you hear the music? That's a 4/4 string ostinato in D minor! Every sailor knows that means death!
Sandy also has one in "Sandy, Spongebob, and the Worm", when she realizes that the thing she tied up was only the worm's tongue.
Star Trek: Lower Decks: In "Envoys", Ensign Sam Rutherford panics and exclaims "Oh, crap!" when he realizes that he must fight a dozen holographic Borg drones because he has no prior combat experience ("I don't know how to fight!").
"The Lawless": Darth Maul's reaction when he realizes that his old masterDarth Sidious has come to Mandalore is a sight to behold:
"I sense a presence, a presence I've not felt since... Master!?"
"The Unknown": When Admiral Trench, debriefing Count Dooku about an unexpected case of Unfriendly Fire among the Republic forces, explains that the clone trooper responsible looked to be in some sort of trance, Dooku is distinctly alarmed, as he realizes that the Sith's plans for Order 66 and the clones' Manchurian Agent status are in danger of being exposed.
"The Bad Batch": Admiral Trench is not happy when informed that the clone strike team who breached the Separatists' Cyber Centre on Anaxes may have made a transmission to Skako Minor, since that's where he's getting his stolen Republic strategy algorithm broadcast from... where it's being forcibly extracted from a captured and thought-dead Republic soldier, ARC trooper Echo.
Star Wars Rebels: In "An Inside Man", Ezra and Kanan are disguised as stormtroopers when the Imperial facility is placed under lockdown. Recurring adversary Agent Kallus orders the two to follow him into a lift. Once inside, they realize Kallus knows who they are. Then immediately subverted when Kallus utters Fulcrum'scode phrase.
One of the biggest ones is when Leonardo is sent crashing through the window of April's apartment, nearly dead. In rage, Raphael is about to leave to find out who was responsible and make them pay, when Leonardo struggles to talk and stops him from leaving. His last words before losing consciousness??
The look of fear and shock on everyone's faces afterwards is amazingly effective.
Thomas the Tank Engine uses this a lot. Each engine model has a scared face that's absolutely perfect for this. Commonly seen when an engine's train becomes a runaway. A good one would be in "Old Iron". James is cruising along light engine (due to some naughty boys climbing into his cab and playing with his controls), enjoying himself. Then he notices he's going faster and faster, and realizes his cab is empty. "What shall I do? I can't stop! HELP! HELP!"
It's generally agreed, however, that the most infamous of all the Oh, Crap! faces is the "O" Face◊.
Time Squad, the main three characters are prone to giving these looks whenever something terrifying is about to go down, for example when an airplane flown by the Wright Brothers or an evil My Little Pony comes charging after them.
In "Hate or Let Hate", Otto is stranded on a deserted island that's only inhabited by baboons. The boy gets cornered by the monkeys, and as he trembles in fear he mutters, "Aw Crud. . ."
The look of pure abject horror on Optimus Prime's face when the restored Megatron (whom he'd thought dead since the first episode) bursts out of Sumdac Tower is priceless. This is a 'bot who understands exactly how completely and utterly screwed he is.
The Elite Guard get a big one when, after insisting for the entire episode that there are no Decepticons on Earth, they face off with Starscream, who is more than willing to show the lot of them a taste of what Optimus has been up against.
Ultra Magnus has a pretty good one. After telling the Autobots to stand back, he presumably intended to deal with the situation. As soon as he turns around, Starscream has recovered and is pointing his weapons right in Magnus's face. *blast!*
Transformers: Prime finally gets in on the action. After doing everything in his power to prevent it, Megatron fails to keep Optimus Prime from obtaining the Star Saber, a legendary weapon that can only be used by a Prime. Prime uses the sword to not only cleave in two a mountain that was just dropped on him, but to fire a Sword Beam at the Decepticon warship. Megatron's reaction is less than positive, as he calls this the Decepticons' darkest hour.
Dr. Venture of The Venture Bros. pretty much whenever he screws up or pisses someone off.
Wacky Races: Dick Dastardly has several, but most memorable was in the episode "The Dipsy Doodle Desert Derby" in which he enlists the assistance of Bubu, a genie he releases from a bottle. Bubu plants the Mean Machine atop a high sand dune, to which Dastardly orders him to put him on the ground. Bubu makes the dune disappear. Dick and Muttley both get an "Oh, crap" look before they drop.
Sadlygrove of Wakfu has a fantastic expression when attempting to escape from a flooding room and his Love Interest Eva appears to have drowned.
In the Winx Club season 2 finale, all good guys present in Realix had this reaction when Bloom ignored Sky and continued to give Darkar the Ultimate Power.
in one early episode of X-Men, the Master Mold attempts to escape from his manufacturing factory when he hears the roar of the river Cable just let loose from a dam. However, he stops and realizes his left foot is still hooked up, letting his last words before the water washes it and the other Sentinels away being "I AM STILL PLUGGED IN!"
Wonder Girl: Listen, uh, Black Beetle. You're totally outnumbered. Open those doors now and we'll go easy on you! Black Beetle: You? Will go easy... on me? Ha ha ha ha ha Ha Ha Ha Ha Ha AHA HA HA HA HA HA!!! Bumblebee: Oh, that is not a good sign!
While not verbal, "Antisocial Pathologies" sees Vandal Savage have a horrified look and break a tablet in half upon hearing the Ultra-Humanite inform him that Granny, thanks to capturing Halo, now has the key to the Anti-Life Equation.