The Dove, a Serial-Killer Killer from the Global Guardians PBEM Universe, incorrectly believed he was the hero in a revenge-driven crime thriller. It honestly never occurred to him that he was the villain of a superheroic version of the standard Police Procedural. The revelation of his actual status in the story caused him to commit suicide.
In "We Are Our Avatars", Asagi Asagiri views the world as a massive video game...when it's really a massive forum game, which upgrades into Genre Savvy whenever any mechanics from video games worm their way into the situation.
Spoony: "Suddenly I've decided that I'm terribly afraid of you."
Don Sebastiano, from the Whateley Universe, thinks that he's in a standard Sky High-esque superhero story, he's the Big Bad and that he and Hekate can do anything they want. Problem is, they're actually in an X-Men-esque superhero story. He's more the Disc One Final Boss, Hekate is his dragon, and he's underestimated the value of politics- without them, he'd be dead or maimed, because he's playing in the same league as a bunch of people who could kill him without any effort and have already gone up against bigger enemies. (Seriously, the Don or Hekate- or both of them- versus Tennyo? No contest.)
This Swedish ChefYouTube video has two Wrong Genre Savvy talking pumpkins. They try to use Briar Patching, advising the Chef to use increasingly bizarre/dangerous implements to smash them, on the assumption that he won't have them. However, this is the Swedish Chef we're talking about, who can always pull a sizable arsenal out of hammerspace.
Atop the Fourth Wall: Linkara in his Comic Book Quickies assumes that reading a text box that says the location of a story is the world's largest flea market, that the giant flea in the panel is the world's largest flea and assumes that the comic's creator doesn't know what a flea market is. The real answer he found was much more, surreal. The flea is the the giant flea marketeating flea. He reacts pretty the much the same way as the audience.