Blight/Derek Powers: Who are you?! Batman/Terry McGinnis: ...You really want to know? Blight: Yes! Batman: You killed my father. (beat) Blight:(irritated) Do you have the slightest idea how little that narrows it down? Batman:Too bad. It's all you get.
Later, in the episode "Speak No Evil", a newly-sentient, speech-capable gorilla named Fingers tracks down the poacher, Van Dyle, who captured him and his mother when he was a baby. Given that Van Dyle is cowering and all but begging for his life (and wouldn't you be?) it's considerably less badass.
Fingers: Where is my mother?! Van Dyle: I p-probably sold her. Fingers:Probably? Van Dyle: I don't know, I don't keep track! Fingers: She was my mother! Van Dyle:(clearly terrified) To me it was just another gorilla.
Zucco: Don't tell me what I gotta worry about. I'm not back in town five minutes— five minutes— and he's on my tail. You don't know the bat. He don't let up! He's the dark angel of death, man, and he wants me! Mook: Why does he want you, boss? Zucco: How should I know?!
Because Zucco killed Dick Grayson's parents and earned a Roaring Rampage of Revenge from Batman and Robin. Of course, Zucco's a member of The Mafia, he's killed plenty before. Of course, Zucco doesn't know that the Grayson's son had grown up to become Robin, so he could've made the connection even if he knew it was over those two people.
Subverted in The New Batman Adventures episode "Joker's Millions". The Joker throws a party that Bruce Wayne attends, Joker offers Wayne some champagne, which Wayne refuses, citing the fact that the last time the two met, Joker threw him off a building. Despite only happening a month ago (in-universe), The Joker doesn't seem to remember the incident at all. It turns out the Joker that Wayne was talking to was a body double in the real Joker's employ.
Zigzagged in The Batman. When Clayface broke into Arkham to get revenge on the Joker, the Joker had no idea who he was. (The Joker had Mind Raped Ethan Bennett, and his Joker Putty formula had turned him into a monster, but the Joker had no idea this had happened.) However, later in the episode, when someone mentioned that Clayface was Bennett, then the Joker remembered. (And in his sick mind, he was pleasantly surprised that what he had done had turned out so well.)
The show's version of the Cluemaster was a former boy genius who was the reigning champion on a quiz game show, until the producer and host engineered his loss to a more marketable girl prodigy champ. Decades later he abducted all three people he blamed for his loss to punish and kill them, and none of them had any idea who he was. Even Batman pointed out that he could have been anything he wanted with his brains, instead of wasting his life obsessing over something the rest of the world neither remembered or cared about.
The first Hunter was Gillecomgain, who was just some farm kid when Demona casually mangled his face after he caught her stealing food. He made a mask to highlight the scars and began hunting her relentlessly. Several decades later, she finally overpowered him and unmasked him before giving the finishing blow. He stared at her and asked if she now understood why he hunted her for so long. Demona flatly replied, "No." This made him angry, of course. After he is killed, Duncan takes up the mask and position of Hunter. Duncan's descendants began a thousand year blood hunt for her, and she still doesn't know why (not that she would care anyway). In a deleted scene from "Hunter's Moon: Part Two", the leader of the latest generation of Hunters confesses to Elisa that no one in his family remembers how or why the hunt began, either.
This was echoed later on with Malcolm Canmore, son of Duncan. Macbeth killed Duncan in battle and banished Canmore to England. Later, Canmore becomes the new Hunter and invades Scotland, eventually unmasking dramatically in front of Macbeth.
Macbeth: Should I have recognized you, sirrah?
Of course, he does remember Canmore, he just doesn't recognize him. It's been over fifteen years since they last met, after all.
On the heroes' side, they had a repeated negative effect on the life of a man named Vinny until he becomes a comic relief villain, and the only person to ever carry out revenge against Goliath to his satisfaction.
In Superman: The Animated Series, Superman finally ends up fighting Darkseid and gives him an And This Is for... punch for Dan Turpin, the man he killed during the Apokolips invasion. Darkseid has no idea who he is talking about and merely exclaims "Had I known one human's death would pain you so, I would have killed more."
Scarlet Witch: We're here to get revenge for one who has fallen in your path. Magneto: You will need to be more specific. There have been many. Quicksilver:It was our mother!(Let's You and Him Fight ensues)
Note that Magneto may not remember the many who "have fallen in his path", but he does remember Magda. In fact, he was paying a visit to her grave right there, before being ambushed.
Princess Azula shows herself to be this type of villain when her plan against her brother begins to take shape in Season 3. You can almost see her going through the exhaustive list in her head of My-Diabolical-Plots-Against-Zuko.
Zuko: Why'd you do it?! (beat) Azula: You're going to have to be a little more specific.
A more humorous version of this happens when Sokka and Zuko travel to the Boiling Rock and run into Suki:
Sokka: Oh, good. You guys have met. Suki: Actually, we met a long time ago. Zuko: We did? Suki: Yeah. You kind of burned down my village. Zuko: Oh. Sorry about that. (beat) Nice to see you again?
This example is a bit odd in that it seems it was a bit of a Tuesday for Zuko and Sokka. While he was obviously present for the whole episode, Sokka apparently remembers Suki but not Zuko setting fire to her village. Maybe justified because Suki gave Sokka his Sacred First Kiss?
Played nearly straight when Katara finally tracks down the man who murdered her mother when she was a child. At first, he has no idea what she's talking about.
One episode has Homer meeting universal Butt Monkey Frank Grimes and driving him to suicide. In a later episode, Frank Grimes Jr. shows up to get revenge. Homer can just barely recall the incident, and actually asks Junior how his father's doing.
Exaggerated between Homer and Mr. Burns. No matter how many messed up, idiotic, and catastrophic things Homer does...Mr Burns still can't remember the name of that buffoon from Sector 7G.
Smithers: That's Homer Simpson, sir. All of the recent events in your life have revolved around him in some way.
Mr. Burns: Simpson, eh?
The "Who Shot Mr. Burns?" two-parter took this to extremes, with Homer breaking into Mr. Burns' office, spraypainting I AM HOMER SIMPSON along his walls in huge neon green letters, and Mr. Burns' response is, "Who the devil are you?" This pushes Homer's Berserk Button.
Homer: (strangling Mr. Burns) HOMER SIMPSON! HOMER SIMPSON! MY NAME IS HOMER SIMPSON!
Mr. Burns: Smithers, who is this idiot strangling me?
Homer: SHUT UP!! HOMER SIMPSON!!
This actually bites Homer in the butt. When Mr. Burns regains consciousness after being shot, all he can say is "Homer Simpson" over and over. Though ironically, he still doesn't recognize Homer.
Parodied/averted in a Halloween episode:
Fortune Teller woman: How's that curse I cursed you with, Cursed-y?
Mysterio: Don't pretend you've forgotten. I was the Chameleon's right-hand man! Spider-man: Oh, right. On the boat! You were...You were dressed as the crewman! Mysterio: As the waiter!
Speaking of whom: The version of Quentin Beck from Spider-Man: The Animated Series became Mysterio to get revenge on Spidey for exposing an unethical stunt he pulled while shooting a movie. He doesn't mention it at first, but when he does Spidey has no idea what he's talking about until Lieutenant Terri Lee looks it up.
Flashback!Beck: They'll arrest me for this, and it's all your fault! I will get you, I swear! Lee:This is something you have trouble remembering? Spidey: Hey, I hear that kinda thing...two, three times a week!
In Justice League Unlimited, Deadman, possessing Wonder Woman, beats the crap out of Devil Ray, telling him that he killed his mentor and friend.
Devil Ray: You'll have to be more specific, lady. I've killed a lotta people.
Although Devil Ray is kind of justified in being confused, since he didn't kill Wonder Woman's mentor.
The Secret Saturdays, Argost when confronted by Drew and Doyle when they discover he was the Yeti that attacked their camp in the Himalayas and murdered their parents. His response?
Argost: *smirks* Did I? Oh, there were so many in those days. One can hardly remember each individual scream.
A heroic example occurs in the Codename: Kids Next Door episode Operation: BULLIES (a parody of Jurassic Park), where Numbuh Four does not remember giving Jerry Rassic the wedgie that destroyed his life back in first grade. Too bad Jerry now has a Wedgiesaurus Rex ...
On Jimmy Two-Shoes, Jimmy finds out that Mr. Ten had been cursed by Heloise, he goes and confronts her about this. Being Heloise, she needs more information, showing Jimmy a long list of people she's cursed.
Chemistro: How can you not know who I am!? You punched me in the face!
Hawkeye: Sorry, that doesn't narrow it down much.
My Little Pony: Friendship Is Magic: Season 4, episode 12, "Pinkie Pride". It turns out that the guest character, Cheese Sandwich, became a wild party pony after having been inspired by one of the parties Pinkie Pie threw as a child.
Not necessarily, this could be the first time Pinkie came to ponyville, the town of which she is now occupant, it was probably a big day for her too.