Oh great, Alice is making one of her "suggestions" again, and Bob is just getting ready to deploy the mandatory response when Alice suddenly begins to make sense. "Hang on!" Bob says. "That's a brilliant idea... why didn't I think of that?"
This is when a character suggests something to another character that they wish they'd thought up, or are even surprised they didn't think up first. Despite the opening this doesn't have to be a previously dim or spacey character surprising a smart one (though that version may overlap with Dumbass Has a Point); simply suggesting something that in hindsight seems obvious can catch any character off guard. Compare Glad I Thought of It, where the character not only wishes they'd come up with the idea but tries to pretend they did come up with the idea.
- In My Hero Academia: The Two Heroes, Kirishima gets smacked into a wall during a fight, and he can't get out because the jagged edges caused by his quirk keep him wedged into the hole.
Kirishima: I'm stuck. Can you guys help get me out of here?
Bakugo: Are you really that stupid? Just turn your damn quirk off, you moron!
Kirishima: ...Oh, right. Gee, why didn't I think of that?
- Oscar Wilde:
Oscar Wilde: I wish I'd said that.
James Abbott McNeill Whistler: You will, Oscar, you will.
- Milton Berle, who was memetically known for stealing other people's jokes, would often use this on himself (and obviously, the bit itself was stolen from Whistler, above).
Berle: (quoting back a punchline that was just said) I wish I'd said that.
Other person: You will!
- In an early Thunderbolts issue, the superhero Citizen V (actually a disguised Captain America supervillain, Baron Zemo) confronts Fantastic Four villain the Mad Thinker, who explains his master plan. "V" responds that "it's a good plan. I see no reason why it wouldn't work. Except, of course, for me."
- Ultimate Spider-Man: Kong wants to fight Crusher Hogan and get five hundred dollars, but the manager did not allow him: he's a minor. Peter made a mask for himself and simply jumped into the arena without asking. Kong was there, and thought that it's what he should had done as well.
- The Sponge Bob Movie Sponge Out Of Water: When our heroes venture to the surface world and see Burger Beard selling Krabby Patties with the formula he stole:
- In RoboCop (2014), this is the response of the OmniCorp PR man to the news that RoboCop is investigating his own murder.
That was an easy joke. I could've thought of it... Why didn't I think of it?
- Played for tearjerker effect in the Dollhouse episode "Epitaph One". The Neural Implanting technology has been weaponized and the United States has collapsed into anarchy after an attack from China. Topher, the scientist who helped develop the technology, is in his Room Full of Crazy and works out how it was done.
Topher: An entire army in a single instant; that's all it takes. That's brilliant! Why didn't I think of that? (sees Adele's expression) Did I think of that? Did I? Oh god... Oh my god... Oh my god...
- In Season 3 of Buffy the Vampire Slayer, Giles is sacked from his position as Watcher and replaced by Wesley, who impresses no one. When Faith meets him for the first time...
Faith: New Watcher?
Buffy and Giles: New Watcher.
Faith: Screw that. (walks out)
Buffy: Now, why didn't I just say that?
- On World's Dumbest..., this is Godfrey's response to seeing people using popsicle sticks to get extra time on parking meters.
- From Wacky Races, after the Mean Machine is crushed by a hillbilly's boulder trap:
Dick Dastardly: Wow! What a keen booby trap! I wish I'd thought of it!
- Futurama, "A Biclops Built For Two"; Fry is in a dungeon:
Fry: Leela, you have to get me out of here. It's horrible! Eating scraps, letting my waste drop where I stand like an animal in the zoo.
Leela: Animals go on the corner.
Fry: The corner! Why didn't I think of that?
- Shaggy says this in the Scooby-Doo episode "Scooby's Night With A Frozen Fright," when Scooby shows him how he hooked a link of hot dogs from the gang's picnic basket.
- In an episode of Aladdin, Genie temporarily gives his powers to Iago, who (contrary to the Jerkass he acts as when an ordinary parrot) goes out of his way to try to improve everyone's lives. After Iago redirects a river, Genie wonders aloud why he never thought of that; Iago uses his newfound genie powers to make a big show opening his head to show off his brain in response. Then all of Iago's benevolence backfires dramatically, showing that maybe it's for the better that Genie didn't ever think of that.
- In Frosty the Snowman when Hocus Pocus suggests to get help from Santa Claus to help Frosty and Karen.
Frosty: That's a great idea. Why didn't I think of that before?
(Hocus glares at him and taps his foot impatiently)
- In the "Flying Sorcerers" arc of Underdog, the King of the Flying Sorcerers has a love of cakes and has Sweet Polly Purebred kidnapped to make him all the cakes he wants. When Underdog rescues her and the king bemoans not getting anymore cakes, Polly gives him a recipe so his people can make cakes without kidnapping chefs, leaving the king to wonder why he didn't think of that in the first place.
- In the Darkwing Duck episode 'Jailbird', when Negaduck uses a mystical gem to steal the powers of his fellow members of the Fearsome Five, he uses Liquidator's water powers to part the bay and make a clear path for him to St Canard.
Liquidator: Say, why didn't I ever think of that?
- In Teenage Mutant Ninja Turtles (2003), when Professor Honeycutt won't build his Teleportal to help the Turtles return to Earth, fearing it would fall into the hands of the Federation or the Triceratons, Donatello foolishly points out that it wouldn't matter as they could just use a Mind Probe in front of the Prime Leader of the Triceratons.
Donatello: What's to stop them from ripping apart your robot body and downloading the data from your brain?Donatello: Sorry.
- The Sylvester the Cat cartoon "Peck Up Your Troubles," has Sylvester trying (and failing) to catch a woodpecker, As he paces back and forth, he suddenly gets an idea. He holds up a sign that says "Why didn't I think of this before?" then starts climbing a flight of invisible stairs towards the tree branch the woodpecker is perched on. (Second sign: "Anything is possible in a cartoon!")
- Thomas Huxley's response to Charles Darwin's theories of natural selection was "How extremely stupid not to have thought of that!"
- Shigeru Miyamoto has gone on record saying that he wishes he had thought of and created Ni GHTS Into Dreams.
- Stephen King was surprised by the Cruel Twist Ending of The Mist, which was based on one of his short stories, and wished he wrote that.