Both times that Doc gets shot in Part I. Marty's reaction might be a little Narmy to some, but...imagine seeing your best friend killed in cold blood, twice, and not being able to do a damn thing about it in either case.
And when George finds Biff with her instead of Marty, the fact that she sounds so terrified.
Lorraine: (tearfully) George, help me! Please!
The moment where Marty starts fading away and George looks like he's about to give up on Lorraine after a Jerkass steals her away during the dance, and Marty weakly, inaudibly pleads to George not to do so as he starts to collapse. It's less than a minute, but the intensity of that moment makes it feel so much longer.
Marty hugging Doc goodbye before trying to get back to 1985. Now more than ever, his mind is on whether his friend will get the message. If he doesn't, this will be the last time he'll see him alive, and Marty knows it. It doesn't help that it looks like he's holding back tears as he says "I hope so...".
Have a couple of tissues ready in Part II when Marty finds George-A's grave…
The scene when Marty receives the letter from Doc can cause some to get misty eyed, the music doesn't help either. It's not sad, it more or less causes tears of joy.
The scene when Jennifer finds out that Marty had a car crash thirty years ago, from racing Needles when he called him a chicken. This crash broke Marty's hand, which left him unable to play guitar very well, and forever crushing his dream of becoming a rock star. Then we see Future!Marty silently playing his guitar.
The song Marty is playing? "The Power of Love" from the first film.
Worse, the Marty from 2015 has turned into a bitter, pathetic man who is vastly different than his seventeen-year-old self that we have all grown to love.
This becomes even more awful when you look at this from Jennifer's perspective. She was excited to find out she and Marty are married, but is panicking about not being seen in her future home. But then she finds out that she never got her dream wedding - cheaping out and getting married in one of those little white chapels. Worse, she overhears that her boyfriend's life ends up going down the toilet, she sees first hand just how much he has changed for the worst in the future, she witnesses his "chicken" problem ruining his life AGAIN as he's fired, and she hears his guitar playing, which was his passion in 1985, sounding terrible. Oh, and the cherry on the cake? Lorraine says herself that she thinks Jennifer only married her son out of pity. Dear God, talk about worrying about the future!Fortunately for both Marty AND Jennifer, this timeline ends up never happening thanks to Marty's Character Development in Part III.
"Besides, they couldn't match up the bullet that killed your old man!"
"You son of a bitch," indeed.
Seeing Lorraine as an all-out Broken Bird/Iron Woobie in 1985-A. She's an alcoholic again, and she's stuck in an abusive marriage with Biff because he murdered George - only staying with him because he'll cut off her children and possibly send them all to jail if she leaves. Especially hits home when Biff pushes Lorraine on the ground, and she's completely helpless.
Not helped by Marty going ballistic when Biff does this.
Marty:(restrained by Biff's mooks)YOU SON OF A BITCH!!
The full reading of Doc's letter (which was started at the end of Part II but never finished), especially since it was intended by Doc to be the final words he ever said to Marty:
"Do not, I repeat, do not attempt to come back here to get me. I am perfectly happy living in the fresh air and the wide-open spaces, and I fear that unnecessary time travel only risks further disruption of the space-time continuum. And please take care of Einstein for me. I know that you will give him a good home. Remember to walk him twice a day, and that he only likes canned dog food. These are my wishes; please respect them and follow them.
And so Marty, I now say farewell and wish you Godspeed. You've been a good, kind, and loyal friend to me. You've made a real difference in my life. I will always treasure our relationship and think on you with fond memories, warm feelings, and a special place in my heart.
Your friend in time,
"Doc" Emmett L. Brown.
September 1, 1885."
Big one in Part III when the DeLorean gets destroyed. Seeing one of the most iconic props in cinema wrecked after it has gone through hell and back and just kept ticking is heartbreaking. The worst part is seeing the flux capacitor and the time interface go out.
Marty:Well, Doc, it's destroyed... just like you wanted.
Seconded. That car was practically a main character by itself. A more faithful vehicle you couldn't hope for. And it was smashed to smithereens like any other piece of junk. When Marty chokes up, we choke up too.
Furthermore, the shot showing the time circuits and flux capacitor fizzling and dying. The analogy of a heart monitor failing and so forth.
A deleted scene in Part III shows Marshall Strickland gunned down by Mad Dog Tannen, right in front of his son. He dies on the spot. It was actually for this reason the scene was taken out, though the event has been confirmed as canon, thanks to the game.
Any scene with Doc and Clara within thirty feet of each other that is not a Crowning Moment of Heartwarming is bound to be a Crowning Moment of Heartbreaking. Case in point: Right before Clara slams the door in Doc's face, she demands to know why he would make up such an elaborate lie about traveling to the future when a simple "I don't love you" would suffice. She slams the door... and cue Doc's big brown puppy-dog eyes filled with pain when he says to the shut door, "But that's not the truth!"
The Telltales Game
Surprisingly enough for this Troper, when Marty first meets with "Citizen Brown Universe" Biff in Episode 3, you find out that Biff is forced to be a good guy and follow all the rules or else. At first, you don't seem sorry for him as now he's not the evil bastard he was like in the past movies and previous episodes, looking to be a changed person for good. But you can tell that he regrets dearly being a Citizen Plus by the way he talks, especially when he gets to the part about giving up his many dogs, you can't help but feel sorry for him.
In Episode 3 it's hard to watch Citizen Brown struggle with what he's done. The road to Hell is paved with good intentions, indeed. Thank God for Doc's notebook...
Episode 5: Citizen Brown Doc being erased from existence as Marty is kneeling next to him.
Episode 5: Having to see the completely rusted and dead De Lorean in Alternate!1931. Its one thing to have to see the car, a staple, a character, an icon, of this franchise get trashed in BTTF 3, but to see it rust off into a wreck, a hollow, decayed and empty shell of its former self, its parts stripped, to make a clunky and rudimentary alarm system, is to several tropes a real punch in the guts. Imagine encountering the long decayed web-covered skeleton of Bugs Bunny, or Mickey Mouse. That's what that scene feels like to several. Even Marty says half-chocked "I hate seeing it like this".