George McFly: Lorraine, my density has bought me to you.
Lorraine Baines: What?
George McFly: Oh, what I meant to say was...
Lorraine Baines: Wait a minute, don't I know you from somewhere?
George McFly: Yes. Yes. I'm George, George McFly. I'm your density. I mean... your destiny.
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George McFly: Last night, Darth Vader came down from planet Vulcan and told me that if I didn't take Lorraine out that he'd melt my brain.
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Marty McFly: Wait a minute, Doc. Ah... Are you telling me you built a time machine... out of a DeLorean?
Dr. Emmett Brown: The way I see it, if you're gonna build a time machine into a car, why not do it with some style?
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[1955 Doc is watching a video of 1985 Doc]
Dr. Emmett Brown: What on Earth's this thing I'm wearing?
Marty McFly: Ah, this, this is a radiation suit.
Dr. Emmett Brown: Radiation suit? Of course, because of all the fallout from the atomic wars.
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[In the past, Marty observes his dad's incompetence]
Marty McFly: Jesus, George, it's a wonder I was ever born.
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Mr. Strickland: You don't have a chance, you're too much like your old man. No McFly ever amounted to anything in the history of Hill Valley.
Marty McFly: Yeah, well, history is gonna change.
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Dr. Emmett Brown: If my calculations are correct, when this baby hits eighty-eight miles per hour... you're gonna see some serious shit.
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[In 1955, Tab and Pepsi Free aren't invented yet]
Lou: You gonna order something, kid?
Marty McFly: Ah, yeah... Give me a Tab.
Lou: Tab? I can't give you a tab unless you order something.
Marty McFly: Alright, give me a Pepsi Free.
Lou: You want a Pepsi, PAL, you're gonna pay for it.
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Goldie Wilson: You wait and see, Mr. Carruthers. I will be mayor. I'll be the most powerful man in Hill Valley. I'm gonna clean up this town.
Lou: [hands him a broom] Good. You can start by sweeping the floor.
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[Dr. Emmet Brown is doubting Marty McFly's story about that he is from the future]
Dr. Emmett Brown: Then tell me, "future boy", who is president in the United States in 1985?
Marty McFly: Ronald Reagan.
Dr. Emmett Brown: Ronald Reagan? The actor?
[chuckles in disbelief]
Dr. Emmett Brown: Who's Vice President? Jerry Lewis?
Marty McFly: What?
Dr. Emmett Brown: I suppose Jane Wyman is the first lady. And Jack Benny is secretary of the treasury. I've had enough practical jokes for one evening. Good night, future boy.
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[Marty McFly comes to his school in 1955]
Marty McFly: Wow, they really cleaned this place up. It looks brand new.
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Marty McFly: Wait a minute, Doc, are you trying to tell me that my mother has got the hots for me?
Dr. Emmett Brown: Precisely.
Marty McFly: Whoa, this is heavy.
Dr. Emmett Brown: There's that word again; "heavy". Why are things so heavy in the future? Is there a problem with the earth's gravitational pull?
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George McFly: Lou. Give me a milk...
[dramatic pause]
George McFly: Chocolate.
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[Marty McFly arrives late for his take-off]
Dr. Emmett Brown: You got no concept of time.
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Dr. Emmett Brown: I'm sure in 1985, plutonium is available at every corner drugstore, but in 1955 it's a little hard to come by.
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Biff Tannen: I have your car towed all the way to your house and all you've got for me is LIGHT beer?
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Marty McFly: [watching a Honeymooners episode in 1955] Hey, hey, I've seen this one. I've seen this one. This is a classic. This is the one where Ralph dresses up as the man from space.
Milton Baines: What do you mean, you've seen this? It's brand new.
Marty McFly: Yeah, well, I saw it on a...
[realizing]
Marty McFly: rerun...
Milton Baines: What's a rerun?
Marty McFly: You'll find out...
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[Stella Baines is Marty's future grandmother]
Stella Baines: Marty, you look so familiar to me. Do I know your mother?
Marty McFly: [turning to look at Lorraine, his mother in the future] Yeah, I think maybe you do...
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[Marty learns the consequences of tampering with the past]
Marty McFly: Sounds pretty heavy.
Dr. Emmett Brown: Weight has nothing to do with it.
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Marty McFly: [introducing his band] We're... uh... we're the Pinheads.
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Marty McFly: [to Uncle Joey as a baby, playing in his playpen] So you're my Uncle Joey. Better get used to these bars, kid.
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George McFly: Do you really think I should swear?
Marty McFly: Yes. Yes, goddamn-it George, swear.
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Dr. Emmett Brown: Oh my God, they found me, I don't know how, but they found me. Run for it Marty.
Marty McFly: Who?
Dr. Emmett Brown: Who do you think, the Libyans.
Marty McFly: Holy shit.
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[Talking about the Time Machine]
Marty McFly: So does it run on regular unleaded gasoline?
Dr. Emmett Brown: Unfortunately no, it needs something with a little more kick - plutonium.
Marty McFly: Plutonium... wait, are you telling me that this sucker is nuclear?
Dr. Emmett Brown: No no no, this sucker's electrical, but it requires a nuclear reaction to generate the 1.21 gigawatts of electricity I need.
Marty McFly: Doc, you don't just walk into a store and buy plutonium... did you rip that off?
Dr. Emmett Brown: Shhhhhh. Of course. From a group of Libyan nationalists. They wanted me to build them a bomb, so I took their plutonium and in turn, gave them a shiny bomb-casing filled with used pinball machine parts.
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Younger Dr. Emmett Brown: [running out of the room] 1.21 gigawatts? 1.21 gigawatts? Great Scott!
Marty McFly: [following] What the hell is a gigawatt?
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[addressing the shocked expressions at the dance after playing a wild guitar solo]
Marty McFly: I guess you guys aren't ready for that, yet. But your kids are gonna love it.
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[Marty and Doc observe George's incompetence in 1955]
Dr. Emmett Brown: Which one's your pop?
Marty McFly: [points him out] That's him.
[they see him getting kicked around by other school bullies]
Dr. Emmett Brown: Maybe you were adopted.
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Marty McFly: That's Strickland? Jesus. Didn't that guy ever have hair?
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Marty McFly: Calvin? Wh... Why do you keep calling me Calvin?
Lorraine Baines: Well, that is your name, isn't it? Calvin Klein? It's written all over your underwear.
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[Thinking that Marty is an alien]
Sherman Peabody: It's already mutated into human form. Shoot it.
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Marty McFly: If you ever have kids and one of them when he's eight years old accidentally sets fire to the living room rug, go easy on him.
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[seeing a poster for the Enchantment Under the Sea dance]
Dr. Emmett Brown: Look. There's a rhythmic ceremonial ritual coming up.
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Dr. Emmett Brown: Have them go on some sort of social...
Marty McFly: You mean like a date?
Dr. Emmett Brown: Right.
Marty McFly: Well, what kind of date? What do kids do in the '50s?
Dr. Emmett Brown: Well, they're your parents you must know them. What are their common interests? What do they like to do together?
Marty McFly: Nothing.
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[The AK-47 has jammed and the VW Micro-bus has stalled]
Lybian #1: Damn Soviet gun.
Lybian #2: Damn German car.
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[is checking to see if all the parts of the time machine are working before he takes off]
Marty McFly: ...Flux-capacitor... fluxing...
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Lorraine Baines: Will I ever see you again?
Marty McFly: I guarantee it.
thanks to imdb.com