Here we just post things in the movies that repeat themselves. I'll start.

At the beginning of Part I

Biff, to George: You realise what'll happen if I had in my reports in your handwriting? I'll get fired.

And in 1955...

Biff: You realise what'll happen if I hand in my homework in your handwriting? I'd get kicked out of school.

http://bttf.wikia.com/wiki/Recurring_gags

I actually posted that article to the website, when it was axed from Wikipedia. I even added the Within Part III and the Catchphrase Count sections. That's one of my favourite aspects of the trilogy.

I like how there there's a family dinner scene in every era of the trilogy. It may not seem like a big deal, and "our" Marty wasn't even present at the 2015 meal scene - but I think it still counts as a recurring gag, plot device, or whatever.

Ok...

Biff/Buford/Griff: I thought I told you never to come in here.

Actually, Griff says: I thought I told you to stay in here! :)

It's almost the same thing

That's true! I always thought they should've had Griff crashing into manure in Part II, though - and Griff harassing a girl, maybe Marlene. That part seemed a little unbalanced.

Marty: Mom, I had a horrible nightmare......

Lorraine: well, you're safe and sound now back in good old 1955.

Marty: 1955? But you're my. you're my.

Lorraine: My name is Lorraine. Lorraine Baines.

Marty: But you're so... thin.


Lorraine: Well, you're safe and sound now, back on the good old 27th floor.

Marty: 27th Floor? But it can't be you.

Lorraine: Of Course it's me, Marty.

Marty: But you're so big.


Maggie: Well, you're safe and sound now on the good old McFly farm.

Marty: McFly farm?

Here are my favourite versions of that scene:

Down With Big Brother

Marty: Mom? Mom, is that you?

Lorraine: There, there, now. Just relax. You've been asleep for almost four hours now.

Marty: I had a horrible nightmare. It was terrible. I dreamed I was in a dystopian world from a novel written by George Orwell.

Lorraine: Well, you're safe and sound, now. Here in the good ol' Ministry of Truth.

Marty: Ministry of Truth! Argh! 'You're my ma - you're my ma.

Lorraine: My name's Lorraine. Lorraine Baines.

Marty: Yeah, but you're, uh, you're so, you're so thin'.

Lorraine: Just relax now, comrade. You've got a big bruise on your head.

When Realities Collide

Marty: Mom? Mom, is that you? I feel so sick and hungry!

Elyse: There, there, now. Just relax. You've been asleep for almost three hours now.

Marty: I had a horrible nightmare. It was terrible. I dreamed I was in a sitcom.

Elyse: Well, you're safe and sound, now Here in the good ol' Keaton household.

Marty: Keaton household! Argh! Well, you're my... you're my... my... Who are you?

Elyse: My name's Keaton. Elyse Keaton.

Marty: Elyse Keaton? Uh, no, you can't be. It's not possible.

Elyse: Just relax now, honey. You've got a big bruise on your head.


Back to the Future Part IV

Marty: Mom? Mom, is that you?

Alice: There, there, now. Just relax. You've been asleep for almost eight hours now.

Marty: I had a horrible nightmare. It was terrible. I dreamed I had a bad altercation with another Tannen - and I was beaten up badly.

Alice: Well, you're safe and sound, now. Here in the good ol' McFly household, on 1470 Oak Lane.

Marty: 1470 Oak Lane! Argh! Well, you're my... you're my... my... Who are you?

Alice: My name's Alice. Alice McFly.

Marty: Alice McFly.

Alice: Just relax now. You've got a big bruise on your head.

In the first movie, the Peabody's try to kill Marty. In the second movie, a black family tries to kill Marty.

In the first movie, people comment about Marty's "life preserver", as Marty steps into Lou's Cafe.

In the third movie, people comment about the outfit 1955 Doc dressed Marty in, as Marty steps into the Palace Saloon.

Interestingly enough, there was no similar scene for when Marty steps into the Cafe '80s in the second movie - but that's because he was dressed as his son.

Also, more of an observation than anything - but did you notice how, in the first movie, only Doc '55 was the one who said "Great Scott"? Doc '85 didn't say it until Part II.