In Empty, Kivan finally confronts the ogre who tortured and murdered his lover, triumphantly announces that he will die for killing her, and is appalled to find that the guy has no idea what he's talking about.
In Wizard Runemaster, when Fleur tells Harry she wants to thank him for "killing the bastard who enslaved her", Harry blithely tells her that doesn't narrow things down any. He killed a lot during the war against the Burning Legion.
Spider-Man: "The Destruction of the Milky Way Galaxy... our Galaxy."
Johnny: "Huh... must be Thursday."
Spider-Man: "I never said I was afraid Agent Hill, nervous yeah. I mean here we are again, going up against impossible odds with a plan that may or may not work, oh and not to mention our planet, excuse me Our Galaxy is hanging in the balance."
In Square One, A Cerberus scientist who had stolen research and had been on the run for years looking over his shoulder thinking they were after him finds out they forgot about him years ago until they finally needed the research back.
Miranda: "Poor little man. To you, the day you scraped up the guts to plant a knife in my back was the bravest and proudest day of your life. But to me? It was Tuesday. I didn't give a damn where you went, and I wouldn't now if you didn't have something I wanted."
In the Pony POV Series, Discord reacts this way to recounting his multiple counts of genocide.
NightmareParadox has been pulling her "Groundhog Day" Loop revenge plan on Dark World!Discord for so long she's forgotten when she started, and reveals she doesn't bother remembering the names of anyone but her main pawns, especially the innocent bystanders who get killed, as shown when she doesn't remember who Poison Apple (Apple Pie's identical twin sister) is, asking if she's her coltfriend when asked how many times she's let her die.
The sadistic mass murdering Mad Doctor Professor Kabuto also has this mentality, viewing his victims as little more than lab rats. Given he refuses to refer to any creature who he has no respect for by their species with a number, it's little surprise.
Ditzy Doo's "Butterflies" story has a more humorous example with this exchange between Sparkler and Prince Blueblood (who's since undergone Character Development in his own story).
Prince Blueblood: You look rather familiar, we've met, haven't we?
Sparkler: Uh... yeah... we had a date... It ended with me chewing you out.
Prince Blueblood: Unfortunately... that doesn't narrow it down as much as I wish it did...
Referenced in the fanfic Naruto: Consequences once Naruto and Hinata find out that Konoha has been destroyed and that the Fire Daimyo committed suicide.
Naruto: For Fire Country, the destruction of the Leaf and the suicide of their leader will probably be the most important day of their lives.
Hinata: Really? So what was it for the both of us?
Naruto: For us...It was Tuesday.
Brought up when Naruto saves Kayo in The Pride. She mentions that he rescued her once before, only for Naruto to ask her to be more specific because "When [he] was a genin, it seemed a week didn't go by without [him] rescuing someone or other."
Also referenced in Naruto: Wrath of the Emperor
Naruto: "You tried, remember?" "And what was the end result? Oh, that's right." He ticked off on his fingers. "Sixteen ANBU dead. Three maimed Jounin. One Sannin missing an arm. And Kakashi Hatake dead. And that was me and Hinata without trying. I am not the same gaki you once knew, Tsunade. You and all of Konoha should do well to remember that. The Akatsuki found out the hard way. You should be thanking me, Senju for eliminating the Akatsuki. Wiping them out was probably the most important event in the history of the Elemental Countries."
—Yield to me, and serve me, and undo some small measure of the harm you have worked to my King, and in return I shall give you news of one you have long wondered for: Emeldir, who journeyed far, and never guesses the fate of her only child—
—Even as you kept your promise to Gorlim, he thinks, and braces for the gloating and cruel mockery his slip must surely call forth, but the name is meaningless to his captor, and the answer but a dismissive — Who?
There is a heroic version in the The Kirita Chronicles. Prior to the Death Game the genderbent version of Kirito, Kirita, met the genderbent version of Asuna, Akio, twice in the real world before Sword Art Online. First she complimented him and the second time she saved him from bullies. While Akio remembers their encounters as they had a huge impact on him, Kirita doesn't until Akio tells her at the end of Chapter 9.
Attelus Kaltos of Secret War has a subversion of this when a local Hammer confronts him for killing his brother. He doesn't remember it at all, after killing so many in the many months past. But is still genuinely sorry for the loss. For a short time at least.
This Trope is Zigzagged in Yu-Gi-Oh! The Thousand Year Door Redux. During his duel against Leopold in Twilight Town, Stan attacks his ace monster Grandsoil the Elemental Lord, making it an And This Is for... attack for Philip (one of Leopold's former victims, the husband of the barmaid at the inn). Leopold doesn't even remember him. (And at this point, after all he has done, Stan really didn't expect him too.) In a much later chapter, however, Leopold searches through some records and looks the name up. When he finds it - and realizes the frivolous nature of offense he had taken the man in for, then he remembers Philip, leading to a Heel Realization for Leopold (coinciding with those of his siblings).