In the online comic released for the Australian Christmas 2011 update of Team Fortress 2, Scout pretty directly tells this to a newspaper reporter, who asks him how it feels to be a hero. "If I'm honest? Feels like a Saturday."
In Boktai DS / Lunar Knights, Lucian goes into a rant on how he's been looking forward to taking Dumas out for killing his beloved Ellen. Dumas' response? "Remember? Tell me, boy...do you recall the name of every cow, chicken, and pig you've ever eaten?" Lucian was much less than amused, even though Dumas, as a vampire, did what felt natural.
Bang Shishigami is the universal Butt Monkey among the whole cast in BlazBlue. Nobody takes him seriously except for his friends, and even then it's not his combat prowess that gets recognized. Bang has a serious grudge against Jin Kisaragi for killing his mentor in the last war. Jin gives him this treatment because he was just carrying out orders, and because... well... it's Bang Shishigami...
A heroic subversion occurs in Baldur's Gate II when Jaheira is confronted by a former slaver who was exposed and imprisoned as a result of her actions. He gets more and more angry when she seems not to remember who he was, but it's actually just an act on her part as she wanted everybody around him to hear his "confession".
Wild ARMs 5. When Greg finally confronts Kartikeya about the murder of his wife and child, Kartikeya has to be reminded which of his victims Greg is talking about.
A hero example with Shepard. In Mass Effect 1, you have the option of letting a criminal named Fist live. If you do, you will find him at the Afterlife Club in Mass Effect 2. He isn't very happy to see you, and one of the responses you can choose is "Whoever you are, you stopped being relevant about 5 minutes after I apparently told you to run." (You can also go the other direction entirely, and tell him you`ll follow him across the galaxy to make sure he stays on the straight-and-narrow, if you have to.)
Played with in the world background. When turian ships fired on human ships to stop them from opening a mass relay and subsequently occupied the world the exploration force had come from, humans called it the First Contact War, their first encounter with any alien species and proving the power of the Alliance Navy. For the turians, it's the Relay 314 Incident. Played with, in that the turians unofficially and grudgingly admit that the fight over the planet was the first real military opposition they'd faced in over a thousand years.
Shepard has this reaction when Jacob admits to working for Cerberus, having to think a for a moment before remembering they'd encountered them a few times during their hunt for Saren. This allows for the retcon that Cerberus is a N.G.O. Superpower instead of a rogue black-ops group, by handwaving it as sketchy intel and Shepard being too preoccupied with catching Saren to investigate further.
Towards the end of Knights of the Old Republic, a Dark Jedi, Darth Bandon, is sent to assassinate the Player Character. One of your dialogue options upon meeting Bandon is to recognize him as one of the Dark Jedi who attacked the Endar Spire at the beginning of the game and tell him that "You killed Trask!" and that you will avenge his death. Bandon, naturally, has no idea which of the many red shirts he slaughtered was called 'Trask', and even worse, most players on their first playthrough have probably long forgotten about Trask, too.
Played with in regards to Juhani, who tells the protagonist about how she was rescued from slavers by Revan, whose kindness inspired her to become a Jedi. Little does she know that the person she's talking to actually is Revan, but cannot recall any of this due to suffering amnesia and having a new identity implanted by the Jedi Council. Of course, one could could wonder if Revan would have recalled this small act of kindness anyway?.
In the Scenario Campaign of Tekken 6, if Kazuya Mishima confronts Leo, she will tell him that he killed her mother.
Kazuya: So, you're seeking vengeance. There are so many of your kind, I've lost track.
Final Fantasy VII. When Cloud first encounters Sephiroth again on the cargo ship departing from Junon, he reminds him about having burned down his hometown. Sephiroth's response is a confused "Who are you?" A subversion is that according to creation materials like the Reunion Files confirm Sephiroth never got over Cloud killing him years earlier and wants to Mind Rape him in revenge, so claiming to not know who he is was a part of that.
In Final Fantasy IX, even though he doesn't reveal it to Zidane directly, Amarant and Zidane met once before the events of the game: Amarant was working as a security guard in Treno when he interrupted Zidane carrying out a heist, and Zidane managed to frame Amarant for the crime as he made his escape, leaving Amarant a wanted criminal. Zidane never acknowledges their shared past, and seems completely oblivious to the impact his actions had on Amarant's life.
In Final Fantasy XII, Evil Twin Gabranth impersonated his brother Basch while murdering the king. He also happened to kill Vaan's brother Reks during the incident. Two years later, when Gabranth confronts the party, everyone is outraged to see the king's murderer while Vaan calls Gabranth out on killing Reks. Gabranth doesn't even appear to hear him.
This happens in Gilgamesh's point of view in Dissidia012. Throughout the series he had been travelling the Final Fantasy multiverse for a rematch against Bartz (his self-proclaimed arch-nemesis) Bartz doesn't even remember him. He then runs into Squall, Zidane, and Vann (Three other characters that met him in their respective games) who also don't remember him. While he assumes this trope is to blame, the truth is actually that they all had most of their memories wiped prior to the endless war. Gilgamesh retained all his memories because he was never officially summoned there, thus avoiding the mind wipe.
Omega Red's ending in Marvel Super Heroes vs. Street Fighter: he's killed Ryu offscreen, and Ken is kneeling next to his corpse and asks Omega Red "How many lives have you ended?". His reply is "Do you count the number of breaths you've taken?"
Hawke: For a slaughtering ground, it's actually rather pretty. Tallis: The Montfort family inherited this mountain from a clan of Nevarran dragon-hunters. Well, maybe inherited is the wrong word. What do you call it when you kill someone in order to get all their stuff? Hawke: Tuesday.
Towards the end of Custom Robo Arena, Eddy confronts Dr. Mars/Scythe in a You Killed My Father moment. Scythe doesn't remember, saying he can't possibly remember all of Greybaum's operations.
Heroic example in Final Fantasy Tactics A2: Ghi Yelghi has idolized Frimelda as a Worthy Opponent ever since she saved his town from destruction. For her, that was just one more adventuring exploit.
A probable meta-example in the Metal Gear series: In the eyes of the players, the best and most defining moments for Solid Snake are the events of the Metal Gear Solid, the Shadow Moses incident, and all of the consequences of it. In-universe, while very important and gained quite a bit of fame thanks to Nastasha, Shadow Moses incident is treated as a massive Unwitting Pawn stepping stone for every Chessmaster's and Magnificent Bastard's checklist, a mere component to the greater plan. For Solid Snake, Outer Heaven is the most defining moment of his life.
A straighter example: For the Philosophers, the death of The Boss is just a necessary sacrifice that can be replaced with Gene. For Naked Snake, this is a moment, and the truth behind it, that changed everything.
In Sakura Taisen V, when Gemini finally catches the villain that killed her mentor and demands her revenge, said villain says "You'll have to forgive me. I've killed far too many to keep count."
In Crash Twinsanity, when confronted by Aku Aku and Uka Uka about why the Evil Twins are destroying the island and seem to have a personal vendetta against him, Cortex replies "I've ruined the lives of so many, I can't be expected to remember them all."
Towards the beginning of Arc The Lad, the title character has the following exchange with the villain:
Arc: You're the one that killed my father!
Ark Ghoul: I have killed many, and your father may have been among them. But if I did slay him, his death was so unremarkable that I have no memory of it.
Sengoku Basara: In the third game's backstory, Date Masamune lost nearly his entire army, almost lost Kojuro and barely escaped from an encounter with Ishida Mitsunari. Masamune proceeds to go absolutely batshit insane in order to chase him down, and when he does, he starts on a massive rant about how he's going to destroy Mitsunari. Then, Mitsunari turns around and asks: "Who are you?" Masamune's reaction is priceless. Masamune then goes on to remind Mitsunari about Odawara, in which case Mitsunari starts reminiscing about the battle, only to say that he defeated someone there, but they weren't worth remembering. Masamune loses it and attacks him.
Bringing Mitsunari to any of Masamune's stages in Free Battle mode results in Masamune gloating about how he's finally got Mitsunari right where he wants him, while Mitsunari, bewildered, asks Yoshitsugu who the heck this person is.
Mitsunari: You... Hate me? Who are you, exactly?
Similarly, Masamune making a scathing comment about the deceased Toyotomi Hideyoshi is enough to make Mitsunari drop everything and focus exclusively on killing him horribly.
Implied to be the case with Maxi's vendetta against Astaroth in Soul Calibur. Maxi has confronted Astaroth multiple times on the massacre of his crew, but...
Maxi: Remember me, you freak?!
Astaroth: Pretentious little bug. You all look the same to me.
Marisa: Whoa, so, do you really drink it? You know, that. Remilia: Of course. But I have a small appetite and leave some behind. Marisa: How many people's blood have you sucked by now? Remilia: Can you remember the number of times you've eaten bread? Marisa: Thirteen. I prefer Japanese food.
Used against the protagonist in Red Dead Redemption. When John Marston, a former bandit, meets a mysterious stranger and asks if they know each other, the stranger claims John has forgotten more important men than him. John disagrees saying that he is good at remembering faces. In response he then asks John if he knows the name Heidi McCort; turns out one of John's bandit friends shot her while they were pulling a robbery together. When John can't recall the incident the stranger plainly states: "Then why would you remember me?"
Actually the truth is much weirder, the mysterious stranger has been implied to be a supernatural being of some sort ranging from God, Satan, Death or even Marston's own conscience, given the ridiculous number of biblical references they shoehorned into three appearances, also, there was the whole "you shot him and he didn't die" thing. Further, his final appearance is on Marston's own ranch... on the exact spot where he is buried in the Playable Epilogue.
Manfred von Karma of Ace Attorney fame apparently has so little regard for his opponents that he doesn't even recognize Phoenix when he sees him outside of court.
von Karma: I beg your pardon, you see, I rarely remember defense attorneys. They are like bugs to me. Needless things, to be crushed.
The same game contains an actual positive example of this as well: Phoenix was set on his path to becoming a lawyer when Edgeworth rose to his defense in a class trial. To Phoenix, who was feeling abandoned and bullied by his classmates and even the teacher, it made a huge impression and changed the course of his life - but the end of the game reveals that years down the road, Edgeworth barely remembers that it happened.
This can easily happen to the PLAYER in Morrowind. The game is filled with caves, mines, ruins and the like, many of which contain a few hostile, generic-looking NPC enemies that can be killed for loot. The game also has many factions with associated quests, some of which involve hunting down and assassinating specific characters. Since the game world is huge and mostly free of plot locked doors it is entirely possible that the assassination target was killed by the players days or weeks ago. Luckily the player character has an excellent memory and is able to tell the quest giver that Bandit Leader #246 is already dead, but many players' memories of the event are likely lost amidst their vast and growing body count.
Mazoga the Orc in Oblivion swore to become a knight and do heroic deeds after seeing her friend Ra'Vindra murdered by Mogens Wind-Shifter. When you help her track down Mogens and take revenge for her friend, he doesn't have a clue who she is.
Forms part of the motivation for the antagonist in the Fallout: New Vegas DLC, Lonesome Road. For the courier, it was an ordinary package like any they'd normally deliver. For Ulysses, it was the package that detonated the nukes stored beneath the Divide, destroying the place he saw as his home, teaching him the power of a single person to reshape the world and sparking off a dangerous obsession.
And if you want the dialog options allow you to play out this trope entirely when speaking with Ulysses.
If you take the job to guard the Silver Rush, one of the potential customers turn out to be a suicide bomber who turns hostile if you don't let him in. Judging from the note you find on his remains, the Van Graffs did something truly terrible against his family, although it doesn't say what. Your fellow guard however will just say "Wonder what that was about?" with no interest at all.
An anti-heroic example from No More Heroes 2: Desperate Struggle: the first boss, Skelter Helter, is attempting to take revenge on Travis for killing his brother at the start of the first game. Travis, however, doesn't remember who he is (and the player likely won't either, considering said brother only actually appeared in the game for about two seconds). Also pulled off on the player, as the Big Bad's motivation is also trying to avenge relatives killed by Travis - the nameless, generic Pizza Butt executives Travis killed to make money for the ranked fights in the first game were his father and brothers.
However, one of Travis' lines just before the Skelter Helter fight ("When you see your brother in Hell, tell him that he's still a douche!") suggests that Travis knew all about it and was just taunting him.
Perhaps unintentionally, Assassin's Creed I implies that this is Altair's attitude toward killing Templars. The synch bar increases as Desmond grows closer to Altair by doing things that Altair remembers doing. However, it does not increase if he kills a Templar, nor even if he kills all sixty of them. In other words, Altair may have killed every single Templar in the Holy Land, and he doesn't even remember it. Just another day at the office.
In a more traditional example, during Assassin's Creed III, Charles Lee sees Connor several times before realising he's the young Mohawk boy whose village he attacked a decade before.
He also only uses powers that in Nocturne were mid-tier at best, further supporting that you're just another Random Encounter for him.
In Fire Emblem: Path of Radiance, it's possible to have the Action Girl Jill confront the Big BadAshnard about the death of General Shiraham, her father: who always struggled in the Daein army and died a rather dishonourable death, no thanks to Ashnard's Dark Chick Petrine. Ashnard's response? "I don't think we ever had a general by that name." Cue the only time in the whole game that Jill completely loses her shit.
Mr. Grimm in Twisted Metal Black is driven insane by being forced to turn to cannibalism during the Vietnam war by a random stranger. Later on, Mr. Grimm says that the man has completely forgotten of the incident.
Given a twist in Mafia II: Toward the end of the game, one of the missions is to kill Tommy Angelo, who informed on his family. If you've played the first game, you know his entire story and what led him up to this moment, and you're bound to feel sympathetic; in fact, this is a replica of the last shot of the first game. However, for Vito, Joe and new players, he's just a guy you kill and then run from the police as usual.
The Batman: Arkham City tie-in comic Unhinged reveals that Joker inverts this, as Batman finds a diary in Joker's cell that reveals he wrote down the name of everyone he killed through memory.
An inversion: the main villain of the first season of The Walking Dead is the owner of a huge cache of supplies that you stole half a game earlier, whose wife and daughter died because you found his car and said "finders keepers". When you finally confront him, you can either admit that by now you've figured out who he is, or admit you've no idea why he wants to kill you. This scene gets really convoluted if you chose not to participate in the looting.
In Pokémon Black 2 and White 2, the rival has a vendetta against Team Plasma for a Purrloin that was stolen five years prior. All the Plasma agents he demands its recovery from point out that Purrloin are insanely common in Unova, they steal Pokemon all the time, and they'd have a hard time tracking a specific stolen Purrloin for five years. Subverted with the Shadow Triad, the ones responsible; they remember it all too well.
Bautista: Ah yes, now that sounds like something I would do...I have killed many fathers and mothers. Taken many children. Faced down many little girls and little boys with guns pointing at me, screaming for revenge. And I tell each and every one of them the same thing: I. Don't. Remember. You.
In Pandora First Contact, the leader of the Imperium forces says this word for word, when discussing a battle that was regarded as particularly hellish.
Heid:“Yeah sure, I’m aware that for some of our guys fighting in this hellhole was a living nightmare and traumatizing experience. But for me... it was Tuesday.”
In Castlevania: Lords of Shadow - Mirror of Fate, Trevor Belmont vows to slay Dracula to avenge his mother's murder. Dracula taunts Trevor, declaring that he's killed many people, and that he doesn't know Trevor's mother. What Dracula doesn't know is that Trevor is actually his and Marie's son. Dracula only learns the truth from the Mirror of Fate after he has already fatally impaled Trevor with his own Combat Cross.