Batman:You killed my parents. Joker: Wait...[chuckles]...what are you talking about? Batman:I made you. But you made me first. Joker: I was a kid when I killed your parents. When I say "I made you", you gotta say "you made me"! How childish can you get?
Fools Of Fortune: The protagonist finally meets the man who murdered his family and burns down his village. He doesn't even remember the event, causing a major Berserk Button for the main character.
When the title character accuses the Dread Pirate Roberts of killing her love, Westley, he replies "It's possible. I kill a lot of people." Then he says he vaguely remembers someone who might have been him, someone who didn't beg for his life but just asked to be spared, because of a woman he loved. He actually knows exactly who she's talking about because he is Westley.
When Inigo finally confronts the six-fingered man he's been hunting his whole life. Rugen does vaguely recall him, however.
"You must be that little Spanish brat I taught a lesson to all those years ago. You've been chasing me your whole life only to fail now? I think that's about the worst thing I've ever heard. How marvelous."
Pirates of the Caribbean has a comedic example, with various women slapping Jack across the cheek, to which he blithely replies either "...I'm not sure I deserved that" or "...I probably deserved that one." The one time he actually remembers why a woman slapped him was because he "borrowed" her ship. He remembers ships but not women.
Earlier in the movie it's subverted when Jack says to Will "You look familiar. Have I threatened you before?" He hadn't, but rather was seeing a resemblance to Will's father whom he knew well.
Once Upon a Time in the West: Ruthless killer Frank is being pursued by a mysterious drifter known only as "Harmonica," but Frank has no idea why, nor can he remember who Harmonica is. Harmonica never reveals his own name; whenever asked, he instead gives names of some of the many people Frank has killed over the years. His final clue is sticking his harmonica in Frank's mouth, which factored into the event that Harmonica wants to avenge.
Oldboy. Oh Dae-su has long forgotten that he witnessed Lee Woo-jin's incestuous relationship with his sister. Unusually, Woo-jin has no illusions about the scale of the incident from Dae-su's point of view, and doesn't actually expect him to remember it.
Freeway Killer begins with William Bonin talking with the mother of one of his victims. When the mother shows him a picture of her son, Bonin nonchalantly says "So many faces, they all just get so...mixed up".
In Pat Garrett And Billy The Kid, a group of gunman try to take on Billy's gang, but get cut to pieces. Billy wonders who they were and says, "I guess it really must have been something personal."
The titular hero of Forrest Gump doesn't seem to notice when people laugh and refuse to believe the events of his life because he never recognized how epic and momentous many of them were. This guy inspired Elvis, saw his college get desegregated at gunpoint, was a Vietnam War hero and peace activist (albeit accidentally), tipped people off about Watergate, was an exercise guru and provided seed money for Apple computers...after all that, creating the smiley face really was just a regular day for him.
In The Quick and the Dead, Ellen's entire motivation in entering the Quick Draw competition is to kill Herod, but Herod has no idea who she is. Given the fact that he last saw her as a child, however, it's understandable that he doesn't recognize her.
Both parodied and subverted in Kung Pow! Enter the Fist when Betty initially doesn't recognize the Chosen One, but does upon seeing his baby booties.
"Sorry. I didn't recognize you without crap in your pants."
The Damned United: Revie is honestly taken aback that Clough has been harboring such a grudge for so long, over an incident he himself didn't even notice. The real-life facts are more ambiguous, but the film adaptation plays the trope straight.
The Big Bad in The Losers doesn't remember setting up the titular team at the beginning of the movie when reminded of it later, as he does this a lot.
Double-subverted in Last Action Hero: the Trapped in TV Land protagonist warns Cowboy Cop Jack Slater (played by Arnold Schwarzenegger) not to trust his Big Bad Friend John Practice (played by F. Murray Abraham) because "he killed Mozart," a reference to Abraham's role in Amadeus. When Practice does eventually betray Slater, Slater repeats the accusation to him, mangling it as "you killed Moe Zart." Practice's response? "Hey, I kill a lot of people. I can't remember half of them."
Subverted in The Decoy Bride. Lara yells at the paparazzi photographer who's hell-bent on getting photographs of her wedding that he's ruining her life, and he answers that "I've ruined plenty of lives. You're nothing special." Later it turns out that he was lying; she is special to him, and he puts a lot more energy into following her around than he does any other celebrity because he's in love with her.
The events of "Space Seed" were this for Kirk in Star Trek II: The Wrath of Khan. As director Nicholas Meyer puts it, "I think when Khan makes his appearance in the story, Kirk is flabbergasted. He did not lie awake thinking about Khan. Khan lay awake thinking about Kirk."
Happens to James Bond in The Spy Who Loved Me, when Soviet spy Anya Amasova questions him about her lover, who Bond had killed during his mission in the opening teaser.
Bond: When someone's behind you on skis at 40 miles per hour trying to put a bullet in your back, you don't always have time to remember a face. In our business, Anya, people get killed. We both know that. So did he. It was either him or me. The answer to the question is yes. I did kill him.
At the end of Dredd, all of the events on the film were just a typical day for Judge Dredd.
In the Soviet adventure / musical comedy Fear Not, I'm With You, a bandit leader orders his henchmen to torture an old peasant (for information he doesn't even know!).
Old man: Beware! This sin Allah won't forgive you!
Bandit: If you only knew how many sins there are on my soul... One more... one less... Neither me, nor Allah would notice.
Played with in City of God. After Lil Ze accidentally kills Benny while they were arguing, Lil Ze blames Rocket for his death, but doesn't do anything to him. Months later, when a photograph Rocket took got leaked by the news studio he works for, Rocket believes Lil Ze will remember him and have him killed. Instead, Lil Ze forces him to take photos of his whole crew, all while seemingly not remembering who Rocket is, as he often asked his men the name of the photographer. After the last day of take pictures, he lets Rocket keep the camera and spared his life, telling him that's what Benny would've wanted. Benny was friends with Rocket and gave him the camera as a gift.