I'm going to nitpick John Mulaney making fun of
Back to the Future, even though I know his premise here is rather purposefully silly & exaggerated for comedic effect, because I do think there's some interesting things that get lost from a cultural perspective.
I think this is where the generation gap begins, because I'm like almost 12 years older than Mulaney, & a lot of context gets lost in that gap maybe. 1st of all, the pitch of the movie was probably very similar to the pitch of a slew of other movies from then, like
The Last Starfighter,
Explorers,
E.T, Time Bandits, WarGames, D.A.R.Y.L, Flight of the Navigator, etc... Sci-fi was in its heyday at this point, & the general notion was that the fans of the Star Wars phenomenon were primarily young boys 12-18. So, there was a clamor in those 80s years to have sci-fi films that now
showed kids from that demographic as their featured players. Everybody was pitching those ideas. It's the next logical evolution of that pop wave
So BTTF's pitch was likely a simple idea of a teen kid accidentally getting tossed back in time and having to get back to the future... from THERE, duh, a play on words, & basically a modernization of a
Connecticut Yankee in King Arthur's Court. Now, you have to devise the literal vehicle by which that happens, which inevitably involves someone who can build a time machine. The hurdle of how Doc & Marty know one another is not that big of a leap as the above bit might suggest. It too is a matter of context of the time.
Doc, who no longer lives in the Brown mansion, is literally living near Marty's little suburban neighborhood. He literally rides to school on a skateboard, and passes by his house routinely, so easily that he often just stops by to use his music gear in the very 1st scene that all this is established. You're shown it, not told. That's how movies do things sometimes.
Interestingly enough, back then, people actually knew who their neighbors were. So it wouldn't be so unusual for Marty to have found out that a guy living on his way to school was a tech wizard, who could maybe help fix his
own electronic music equipment from time to time. That's how they know each other. Common interests.
It's a small town with like one high school, that nobody ever leaves apparently, & Doc is the resident weird guy who knows a ton about tech. I wouldn't call him a disgraced nuclear physicist either, more like a failed inventor with a masters in some kind of engineering or applied science. Dude, when I was a teen & early 20s, I knew several people outside my age range who were older college burnouts with some kind of weird degree & knowledge in a subject. They were like the MOST fun people to know lol
This really isn't that weird imho. Maybe NOW it would be a weird friendship, in this helicopter parenting age, but back then, not so much, man.