Those who wish to try this in Chuubo's Marvelous Wish-Granting Engine would be advised to invest in either Fist-Shake or (Overacted) Speechlessness XP. In the canon characters, the clearest example would be the Idol, Soun Shounen, who once punched out an ambassador because he thought the party was for him.
The Beholder race from Dungeons & Dragons, combined with a heaping helping of Fantastic Racism. A typical Beholder's world view: It is the pinnacle of creation and the perfect reflection of the Great Mother that spawned their race. Other Beholders of the same breed are tolerable inferiors who have their uses. Beholders of other breeds are disgusting abominations against nature that must be destroyed on sight. Anything that's not a Beholder is barely worth considering — either flies to be swatted when they become a nuisance, or potential slaves. For added fun, although the difference between Beholder breeds is sometimes quite large, other times it can be things so minuscule that nothing that's not a Beholder would even notice. The Beholder with slightly bumpier skin or a different number of teeth is as much a hated inferior as the one who has flame-based powers instead of the standard Beholder suite or has a differing number of eyestalks.
In fact, at least one splat claims that every single Beholder is technically its own breed, and siblings will soon attempt to kill each other over, say, a particular spot or mole.
And the Great Mother? Whose true appearance could solve this issue with a single glance? Any Beholder who sees the Great Mother sees a perfect copy of themselves. It doesn't help that she's completely insane, and is trying to displace all other forms of life with mirrors of herself.
Malfeas in Exalted is a particularly impressive example. The Demon City has to suffer a psychic fracture to comprehend that other people might exist independent of His goals and desires.
Only in the grip of true madness can Malfeas consider the terrible possibility that the universe might contain more perspectives than his own.
His fetich soul (a sort of living Soul Jar) Ligier is very similar: his Motivation boils down to "share my glory with all of existence," while his Intimacies (the things he cares about, whether positive or negative) are all related to the things he's created as an Ultimate Blacksmith. In other words, as a matter of game mechanics, he literally does not particularly care one way or another about anything that is not directly related to himself.
The Dark Eldar Archon Vhane Kyharc is noted to be a narcissist even by their standards, starting by first making the elite of his Kabal get their faces surgically altered to look like his (Dark Eldar society being what it is, it's a good precaution against assassination), then the rest of it (the Half-born, grown in vats to keep a strong population, instead wear masks of his face). The crowning moment would be infecting a planet with a virus that gave every living thing his face.
In the backstory, a lot of the Primarchs have this problem, especially the ones who end up falling to Chaos. There's just something about being fifteen feet tall, the son of what is functionally a god, the leader of an army of bio-enhanced supermen, and praised across the galaxy that leads to swollen egos.
Over in Warhammer, we have Malekith, the Witch King. In the Time of Legends books dealing with the Sundering, when he moves into full-on obsession mode over the Phoenix Throne, he will do literally anything to get what he believes is his due - barter with cults, assassinate the elected Phoenix King, wage a war that pushes Ulthuan to the edge of destruction, unravel the magical vortex keeping the daemons at bay, it doesn't matter, as long as he gets to sit on the throne at the end of it (or, if he doesn't get the throne, nobody else can either). Even when he does realise he's been definitively rejected from consideration, it's an Ignored Epiphany and it takes him a matter of hours to get back into full give-me-the-throne-or-die mode.
In Changeling: The Lost, the True Fae basically make themselves exist through narratives, so they're constitutionally incapable of seeing the world as anything but a story with themselves as the main character. If a Fae's mind strays too close to the notion that other people might actually be people, it goes a bit insane and loses its powers until the thought dissipates.