At the end of Young Justice: Sins of Youth, Klarion (bum bum BUM) the Witch Boy swears that "everyone on Earth has been restored to their normal selves.", prompting Batman to say "'On Earth...' Odd phrasing." As it turns out, Klarion was telling the truth... but alien bounty hunter Lobo, who was off-world throughout the ordeal, soon turned up on Earth looking for the fraggin' bastitch that turned him into a teenager.
DC Comics covers from the Silver Age often include amazing premises (e.g., the hero Killed Off for Real!) accompanied by promises like "Not a hoax! Not a dream! Not an imaginary story!" Invariably, the promise turns out to be literally true, but not specific enough to cover the cheap trick they did use (e.g., an alternate universe.)
An X-Men cover promised that the heralded Death of Professor X! was "Not a hoax! Not a dream! Not an imaginary tale! This is for real!" It was actually true... for that particular story, anyway. A retcon later made it exactly what they said it wasn't — an In-Universe hoax.note X-Men #42 (1968)
Marvel Team-Up had a story where Aunt May was the herald of Galactus. The cover promised "Not a hoax! Not a What If! Not an Imaginary Story!" That denial was specific enough to exclude dreams, which of course it turned out to be.
Joe Quesadaclaimed that Spider-Man's unmasking would not be undone by a "magic retcon". One More Day then proceeded to use magic to conceal his identity (as well as undo a very-well established relationship between him and Mary Jane, which Joe hated).
In Transmetropolitan, Spider Jerusalem starts watching porn based around his persona, preceded by this disclaimer: "This Is a Work of Fiction not intended to represent anyone living, dead or writing a weekly column for a newspaper."
Was Empowered ever spanked by Sistah Spooky? She doesn't want to comment.
In volume 4 of Scott Pilgrim, Scott is leaving his house when he randomly runs into his Stalker with a Crush ex-girlfriend Knives, who greets him with "H-hi! I'm not even stalking you!"
Ramona is also guilty of this in Volume 2 when talking to Scott about Lucas.
Ramona And I didn't even string him along or cheat on him with any cocky pretty boys.
Hopefully not the case with Dori Seda. "No, I don't fuck my dog."
When Batgirl wakes up in a hospital, being tended to by her own mother.
"Thank you...registered nurse I've never met."
In All Fall Down, AIQ Squared give us, "Nothing *on Earth* is unlawful about what's taking place."
In The Cowboy Wally Show by Kyle Baker, the titular Cowboy Wally and his friend Lenny is arrested, so Wally has his lawyer tell the judge "The evidence against my clients is circumstantial, and the girls brought their own drugs and Wally and Lenny didn't know it was a laundromat, and the pony was there when they arrived". Unfortunately, as it would turn out, they were only arrested for peeing in an alley, which is a $100 fine, but now the judge is curious...
In one issue of Justice League International, the team is on a recruiting drive, during which they ask the various people under consideration some basic questions. In a likely Shout-Out to Stripes, they ask The Creeper if he's ever been convicted of a crime, The Creeper scratches his chin and says, vaguely, "Convicted? I don't think I was ever actually convicted."
Baphomet decapitates The Morrigan in Issue #2 of The Wicked + The Divine. Her head then proceeds to sing his praises, make bad puns and declare that "Baphomet is definitely not fucking with you!". He was - the head was fake.