Sherman: It's already mutated into human form, shoot it!
Peabody: *fires a shotgun* Take that, you mutatin' son of a bitch!
When Marty and 1955 Doc go looking for Marty's father.
Doc: Now, which one's your pop?
Marty: (with a grimaced expression, raises his arm, one finger pointed off camera. Doc looks) That's him.
(scene then cuts to Biff's gang surrounding George, mercilessly kicking him as George cheerfully tries to go along with it and begs them to stop, due to a piece of paper taped to his back reading "KICK ME")
Doc: (with a somber expression on his face) Maybe you were adopted...
(Strickland walks in as Biff's gang leave George a wreck.)
Marty: Hey, that's Strickland! Je-sus, didn't that guy ever have hair?
Strickland: Shape up, man! [tears the "Kick Me" sheet off George's back] You're a slacker! Do you want to be a slacker for the rest of your life?
Doc: (dumbfounded) What did your mother ever see in that kid?
Marty: I don't know, Doc. I guess she felt sorry when her dad hit him with the car....hit me with the car.
And Marty (understandably) freaking out at the car vanishing is hilarious to watch:
Marty: Jesus Christ. Jesus Christ, Doc, you disintegrated Einstein!
Doc: Calm down, Marty. I didn't disintegrate anything. The molecular structure of both Einstein and the car are completely intact!
Marty: ...THEN WHERE THE HELL ARE THEY?!
Doc: The appropriate question is, "When the hell are they?" You see, Einstein has just become the world's first time traveler! I sent him into the future! One minute into the future to be exact! And at precisely 1:21 a.m. and zero seconds, we shall catch up with him and the time machine.
Marty:(beat)...Wait a minute. Wait a minute, Doc. Ah...Are you telling me you built a time machine...out of a DeLorean?!
Doc: The way I see it, if you're gonna build a car into a time machine, why not do it with some style?
Not to mention Marty using a Walkman with a Van Halen tape as an Agony Beam, and in the extended version of the scene (available on the 25th anniversary DVD) passing off a hairdryer as a brain-melting gun. And the Brick Joke that Marty knocks George out with chloroform, and in the next scene George says he missed school because he overslept.
Marty's little comment after he tries to get George to ask Lorraine out.
Marty: It's a wonder I was even born. George: What?
Marty finally meets his Uncle Joey, the future jailbird, who is still a baby at this point in time:
"So you're my uncle Joey. [taps the bars on the side of Joey's crib] Better get used to these bars, kid."
Near the mid-point of the film Doc and Marty work out how they're going to get George and Lorraine together... only for Lorraine to turn up at Doc's house and tell Marty that a real man stands up for the woman he loves.note Marty had just punched out Biff at Lou's Cafe. As she's saying this, Doc leans forward onto the covered DeLorean in what can be only be described as a full-body Facepalm.
Blink and you will miss it: The DeLorean is equipped with Goodyears tires.
A deleted scene, viewable in the various DVD and Blu-Ray releases:
Marty: You know, this is the kind of thing that could screw me up permanently. What if I go back to the future and I end up bein'... gay?
Another deleted scene shows Marty peeking into a classroom window and seeing Lorraine cheating on a test. Even funnier is a joke version of the scene, in which Michael J. Fox shows up in a wifebeater, a hairnet, and a cigarette - and acts like a stereotypical Latino thug. "SUNUVA BITCH, SHE CHEATIN', MANG!"
"My God! Do you know what this means? ...It means that THIS DAMN THING DOESN'T WORK AT ALL!"
Funnier thing is: It did work, given that he pulled "Coast Guard" (instead of, say, Navy).
The flaming wind-up car running off the table and setting fire to some old rag. Doc's reaction◊ is priceless.
This is after he has apologized (quite seriously) for the "crudity" of the model he's built because he hasn't made it to scale or painted it. It is otherwise a large and absolutely flawless model of the area around the clocktower, and as detailed as a miniature film set.
The part when Marty tries to get directions from the guy in the cafe:
Cafe Guy:*interrupting* Are you gonna order something, kid?!
Marty: Uh, yeah. Give me a Tab.
Cafe Guy: I can't give you a tab unless you order something.
Marty: Okay, give me a Pepsi Free.
Cafe Guy: You want a Pepsi, pal, you gotta pay for it!
And after that bit, Marty realizes he's sitting next to his future father. After Biff and his gang stop by to harass and torment George, we get a hilarious shot of George staring straight ahead, trying his hardest to ignore Marty as he slowly leans farther and farther forward to stare at George's face with a "holy shit" expression.
"Lou, give me a milk! (dramatic pause) Chocolate!"
And the outtake where the glass slides too close to the edge of the counter, missing Crispin Glover's hand entirely and ricocheting to the floor.
"I'm your density."
That whole scene is just hilarious. The way he awkwardly approaches Lorraine, holding his notebook out halfway over the table, and then Lorraine and her friends staring blankly at him as he breathes, "Density... has bought me to you." And she responds with a flat "What?"
Marty explains that the plan to get his mother and father back together worked like a charm, even Biff was laid out in one punch. His father never stood up to him in his life. Doc contemplates this for a moment on how it might affect history, then shrugs it off. Seeing as he was so adamant about not changing history it comes off as "Well serves him right."
Fridge Brilliance: You could easily point to that moment as Doc working it out that Marty just had HIS life altered via George standing up to Biff, and there were seemingly no dire consequences. So he figures "what the hell?" and pieces together Marty's letter of warning.
Also Doc sees how pathetic George really was, so he believes it might be for the best.
The whole Running Gag involving Marty's vest and everyone mistaking it for a life jacket.
One of Biff's goons: The dork thinks he's gonna drown!
The "Who's president in 1985?" exchange is just outright hilarious because of Doc's hamminess.
50s Doc: Who's President of the United States in 1985?
Marty: Ronald Reagan.
50s Doc:Ronald Reagan? The actor? Then who's Vice President? Jerry Lewis?! I suppose Jane Wyman is the First Lady! And Jack Benny is secretary of the treasury!
And later, once Marty shows Doc his 'portable television studio' (camcorder):
50s Doc: A portable television! No wonder your president is an actor, he needs to look good on television!
Marty's cover of "Johnny B. Goode": not the performance itself or the EPIC guitar solo, but everybody's reactions to it. The band give him concerned looks and gradually stop playing their instruments as Marty goes into a full-blown heavy metal solo (complete with playing his guitar behind his head, kicking over the amplifier and flailing around on the floor) - and when he is done, he opens his eyes...to see the audience silently staring at him like he's a lunatic.
Marty is talking with George while trying (and failing) to figure out how to open a glass Pepsi bottle (he seems to be trying to twist the cap off). George finally gets frustrated with watching this and grabs the bottle from Marty, popping the top off with a nearby wall-mounted bottle opener and handing it back to him.
A blooper version of Marty heading to school at the beginning. He kicks Doc's gate open...only it won't shut again, so he just throws his skateboard at it and runs away. Eagle-eyed viewers can see him starting to laugh as he leaves the camera shot.
Doc about what would happen if Jennifer meets her future self:
Doc: I foresee two possibilities. One, coming face to face with herself 30 years older would put her into shock and she'd simply pass out. Or two, the encounter could create a time paradox, the results of which could cause a chain reaction that would unravel the very fabric of the space time continuum, and destroy the entire universe! Granted, that's a worst-case scenario. The destruction might in fact be very localized, limited to merely our own galaxy.
Marty: Well, that's a relief.
The part where the two Jennifers meet can also cause laughs. They gasp in unison, exclaim, "I'M OLD!" and, "I'M YOUNG!" at the same time, and faint in unison.
In the future, a scene occurs which mimics the manure truck scene mentioned above, only Griff (Biff's grandson) is the victim. Future Biff is a bystander and comments "There's something very familiar about all this."
Even better, in 1955. Future Biff is hanging back, waiting for his moment to talk to 1955 Biff. He overhears young Biff and the mechanic talking about the first manure encounter. Biff says "The manure! I remember that," and he sounds amused by the memory. Between that and his correcting young Biff on his malapropism, that timeline's Biff was able to achieve a pretty decent level of maturity as he aged.
"I think he took his wallet."
Strickland scolds Biff for putting alcohol in the punch, and then he goes into his office and has a drink himself.
The entire scene between old and young Biff.
1955 Biff: Now why don't you make like a tree, and get out of here!
Doc: It's remarkable that Old Biff would have chosen that particular date! It's almost as though that day is central somehow, as though it were the focal point of the entire space-time continuum! *beat* On the other hand, it could just be an amazing coincidence.
The 2015 dog-walker.
"Do we become assholes or something?" coupled with the look on Doc's face as if he's thinking about for a second.
I kinda like that he responds by saying Marty and Jennifer turn out fine, which we find out later is a complete lie.
Marty pulls the Newspaper Dating trick, only to find out it's alternate-1985 Mr Strickland's porch. The first thing he says, carrying a loaded shotgun and pointing it at Marty? "So you're the son of a bitch who's been stealing my newspapers!"
The Jaws19 ("This time, it's really, really personal") ad and its holographic shark. Marty screams in horror as it comes at him, and when it disappears...
Marty: The shark still looks fake...
Jennifer expresses excitement at the thought of seeing hers and Marty's wedding when taking her first ride in the time machine. This excitement deflates after she finds a picture of them as newlyweds.
Jennifer: I get married in the Chapel O'Love?! I gotta get out of here. (drops the picture on the ground and heads for the door)
Not only did Marty cheap out on where to hold the wedding, but he wore a shirt with a tuxedo pattern instead of a suit, and Jennifer wore a ridiculously short dress.
The part in the outtakes when the Western Union man accidentally traps part of his jacket in his car's door.
While the Running Gag of Marty being called chicken was done a lot, special mention goes to Old Marty when Needles dares him to do something illegal.
Old Marty: Nobody calls me chicken Needles. NOBODY!!!
Also the first time that trope shows up, when Griff and his gang calls him that.
Marty to his half-conscious future son after witnessing him getting nearly pulverized by Griff, then deciding to handle him himself:
"Stay down and shut up!"
Doc gives money to Marty for buying 50s clothes, and tells him to buy "something inconspicuous!" One Gilligan Cut later, Marty is outside Biff's grandma's house with his walkie-talkie, wearing a not-so-inconspicuous leather jacket and a Blues Brothers-esque hat and shades combination.
When Marty takes the Almanac from a KO'd Biff (after being punched out by George), the latter wakes up just in time to see Marty reaching into his pocket. Marty's response? He punches Biff in the face to knock him unconscious again. Bearing in mind that he is surrounded by a crowd of onlookers.
Doc spilling the truth about the future after losing Clara.
Cowboy: Do people still walk or run in the future?
Doc: Of course we do, but for recreation. For fun.
Cowboy: Run for fun? What the hell kind of fun is that?!
The fact that Doc tells Marty the cardboard Indians at the drive-in won't be there in 1885 when he drives the DeLorean towards the movie screen... except they are, and they're REAL.
Marty running away from the bear is pure slapstick.
The old-timers' reaction to seeing Marty in his goofy pink "Western" outfit:
Old-Timer #1: Take a look and see what just breezed in the door.
Old-Timer #2: Well, I didn't know the circus was in town!
Old-Timer #3: Musta gotten that shirt off'n a dead Chinee.
When Marty identifies Buford Tannen as "Mad Dog" Tannen, everybody in the saloon either runs away or hides under the tables.
Then Buford makes Marty "dance" (read: force him to constantly dodge bullets getting shot at his feet), and Marty ends it with a moonwalk - you can even hear him singing "Billie Jean" under his breath. Buford's WTF look really sells it.
Doc handwaving away the moral complications to train theft: "We're going to hija—borrow the locomotive..."
Also a brief Heroic BSOD when Doc momentarily remembers how he unintentionally changed history:
Doc: We'll drive the train towards Clayton...Shonash Ravine.
And in the end, after Marty gets back to 1985, we see the ravine is called "Eastwood Ravine".
1955!Doc reading the letter from 1885!Doc.
Doc: "Please take care of Einstein for me. Einstein?!"
Marty: "It's your dog, Doc."
At the end of the same letter, 1885 Doc's rather heartfelt farewell to Marty is considered an in-universe Heartwarming Moment by Marty...and Doc's younger self. "I never knew I could write anything so touching." "I know, Doc, it's beautiful."
When Clara asks the Barbed Wire Salesman if Doc was the man suffering heartbreak at the saloon, she manages to blurt out a rather flattering description of him (could also belong under Heartwarming Moments).
One of the outtakes has Seamus McFly bring home a plush Roger Rabbit for supper.
In another, Doc's goodbye to Clara gets interrupted by the horse farting, which Christopher Lloyd acknowledges without breaking character.
(completely serious) I've come to say goodbye. We both have.
The Roger Rabbit outtake may be funnier when you consider that Christopher Lloyd was in both movies, playing wildly different characters.
When examining the 1931 Newspaper in the inventory which changes from Doc being killed on the courthouse steps to being killed on a paddywagon, Marty's comment will most likely echo the gamers comment.
Marty: Now that's just not fair!
The sequence where Emmett and Edna trade insults in Episode 2 while Doc rescues Einstein from the courthouse roof.
In Episode 3, Marty has to distract a brainwashed Biff, which is accomplished by pointing out various nearby objects.
Early on in Episode 4, Citizen Brown is strapped to a wheeled bench right in front of a giant speaker while Edna and a guard look on. Marty plugs his guitar into the speaker, then jumps down onto the bench dramatically intending to play a loud chord and blast himself clean out the door with Brown. He hits the strings... and only moves a few inches, completely subverting the awesomeness of the maneuver.
Marty: Okay, that was a little less dramatic than I'd expected.
In Episode 4 Marty informs Doc that his alias at the moment is Carl Sagan.
Future!Marty: Bring [Marty] along too! This concerns all of us!
Marty: What does you mean? Does something happen to us?
Doc: Do we turn into assholes or something?
Heck, this whole scene is a hilarious Up to Eleven parody of the first movie's ending. Three Martys, with three DeLoreans, from three alternate futures show up, and immediately start bickering over which one of their timelines is the most important, and which one Doc should be helping - all voiced by MICHAEL J. FOX, no less! Doc and Present!Marty's reactions? They leave in their own time machine.
If you examine the mop in Episode 5:
Marty: The top of a mop. I can flop it on a cop. I can swap it for a top. I can...I think I'll stop.
When refreshing 1800s!Edna's memory of what happened, there are various prompts you have to give, various questions to answer - and there are, as usual for the genre, several wrong guesses included. But when the time comes to remind her of the villainous saloon owner's last name, the only option is Tannen.
In episode 1, at a certain point you can ask Doc about Kid Tannen. He explains that Kid will be serving a life sentence in prison in the near future within 1931. This conversation prompts:
Marty: Wait, if Biff will be born in 1938...
Doc: As I recall, he escaped in 1937 for about three hours.
In Episode 2, when Doc disguises Marty as a 1930s mobster, he tells him that the fake mustache is essential to not being recognized, and that he is easy to disguise with his "nondescript features". The lingering look of disappointment on Marty's face when Doc says this is good for a laugh. Along with him muttering "nondescript...?"
This is referenced later in the same episode, if you ask Zane to draw a caricature of Marty. He comments that it doesn't really look like him, and Zane replies that "there wasn't much to work with".