Carl Barks's comic story "Only a Poor Old Man" had Uncle Scrooge lecturing Donald Duck on how Donald would be more secure if he had wealth. While making sure a mouse didn't eat his dollar bills.
Don Rosa's "Gyro's First Invention" has Scrooge lecturing Gyro Gearloose on the dangers of overvaluing his first invention: "What sentimental rubbish is that?! You can't base your whole career on such a small achievement! You won't get far in life with such a warped sense of proportions!" — all while carefully restoring his Number One Dime to its pedestal.
That's a recurring joke, too. In another Don Rosa comic, "The Treasury of Croesus", Scrooge uncovers the money bin of king Croesus, who had left a room for his first coin. A historian comments: "Who would have guessed someone would be crazy enough to consider a single coin his greatest treasure?" Scrooge isn't amused.
Another Don Rosa's story features the running gag of the three nephews complaining that everyone but Donald consider them identical in looks and actions... While saying the very same words and making the same actions at the same time. To be fair, there are some differences, but they are so tiny that only they themselves and Donald (who in the story is revealed to have a very good sight and a near-impossible ability to check for details) can see them.
In an early issue of Young Justice, Impulse, who acts without forethought or afterthought 100% of the time, said "Boy, don't you hate it when people go off and do whatever they feel like?" after Superboy headed out to confront a villain alone.
Blue Beetle: ...Yeah... besides, who'd ever buy a super-hero called the "Green Batman"? I mean, that's as bad as—
Batman: The Blue Beetle?
Blue Beetle: Well... um... ah...
Early in Watchmen, Rorschach, shown as the biggest wingnut of the lot, laments the sad mental condition of his retired superhero colleagues.
One Les Pretend strip in The Beano had Les's dad discussing the daft things Les pretended to be with his friends, and them all laughing about it. It was at the end of this strip that we first learnt that Les's dad and his friends are all Elvis impersonators.
In Astérix and the Normans, Asterix and Obelix are ordered by Chief Vitalstatistix to see what a group of Norman invaders are doing in Gaul. On their return, Obelix reports to the chief that the Normans all "had such funny names, all ending in -af, like Nescaf, Decaf and Autograf!" Vitalstatistix is highly amused, and says to the other Gaulish villagers: "Ha ha! Did you hear that, Cacofonix, Geriatrix, Operatix, Acoustix, Polyphonix and Harmonix?"
While Clark and Lois were debating how to explain his absence during his death (don't ask, long story), Clark suggested several extremely stupid explanations, including riptides and alien abductions. When Lois asked him what idiots would buy such pathetic excuses, he said: "You did."
The scene in 52, when Clark leapt off a building (he was depowered at the time, which is another long story) to get an interview with a new superhero. Lois wasn't happy about it. Clark pointed out that she used to do the same thing and could "write the book on it".
In an issue of Global Frequency a man claiming to be a magician (as in a proper one) is brought in, and claims that magic is a 'psychological discipline'. One of the people he's working with, a parapsychologist, makes a sneering comment about this. The magician is amused by the parapsychologist's superiority, pointing out that it's not as if her field is part of the rational orthodoxy. The parapsychologist is less amused by this.
Occurs fairly frequently in Dork Tower, either when the characters are complaining about a behavior they also embody, or when they're Leaning on the Fourth Wall about John Kovalic's writing or art.
In one panel of Gotham City Sirens, Batman makes a teeth-baringly horrific face while telling Riddler, "You're not helping people by scaring them."
In The Smurfs comic book story (and Animated Adaptation) "King Smurf", the title character admonishes his captain of the guard, Hefty Smurf, for failing to have a sense of humor when dealing with Jokey playing one of his usual "surprise" jokes on him. Then after King Smurf pardons Jokey, he becomes the victim of Jokey's prank and immediately has the prankster sent to prison.
A holiday special based on the Clerks universe has comic book shop owners Steve-Dave and Walt head to the Quick-Stop because that's the only open store and Steve-Dave needs to pick up some Scotch tape to wrap up some last-minute gifts. As he proceeds to berate Dante for charging what he feels is an outrageous price for the tape, another costumer recognizes him and asks if he has any issues of a new title that just came out, to which Steve-Dave replies that it'll cost him $20.
Creature Tech has a scene where a mother chastises her husband for saying "hell" in front of the children. Then a monster threatens one of her children, and she flips into Mama Bear mode, shouting "Get your hands off my baby, you son of a bitch!"
A rather dark example in Huntress: Year One: Barbara Gordon and two colleagues from the justice department are attending a conference on organized crime in Italy when the news comes out of the murder of notorious crime boss, Capo di Tutti Capi Stephen Mandragora, and they toast his death at a local bar. A woman at the bar berates them for this, saying "Never toast someone's death," and that "it's naive to think death solves anything." All of which sounds quite reasonable, except that the woman at the bar, Helena Bertinelli, the Huntress, is the one who killed him!
In Sonic the Comic Chaotix Crew member Vector constantly yells at Charmy. (When Charmy mentioned this, Vector said that was "Ridiculous! I NEVER YELL AT YOU!")