5. Finally delivering that letter from the 1800s and having Marty ACTUALLY be there to receive it would be a much bigger deal.
Imagine you get a job at Western Union and you find out that the office you work for has been holding onto a letter from 1885 with the instruction to give it to a teenager who will be standing in a specific spot, at a specific time in 1955. 70 years worth of Western Union employees have no doubt heard the tale of this letter and wondered if that fated teen would indeed be in that specific spot at that specific time to receive the letter. When that day finally came around in 1955 when Western Union was scheduled to deliver this letter, there damn well would have been a bigger fuss.
6. Wouldn't Biff using the sports almanac from the future to help him gamble eventually change the outcome of the bets?
To get as wealthy as Biff is in the horrible alternate 1985 would require that he used that almanac to bet on every game and always win. After a certain number of wins, people would start to notice. Here are some very obvious things that would screw up Biff's wins: 1. athletes would find out that the "always wins" guy had bet against them and they would try harder, 2. other gamblers would copy the "always wins" guy's choices and reduce the amount they all won, or, 3. Biff would be barred from placing bets because he was clearly cheating.
7. If George McFly hadn't landed a super lucky strong punch, Biff would've just raped Marty's mom? Really thin margin for error there.
It's one thing to know that your entire existence hangs on your dweebie teenage father's ability to knock out a giant meathead in one punch. That's pretty heavy stuff. But to find out that the strength of that punch is also the only thing stopping awful Biff from raping your mom in a high school parking lot? Jesus. Marty should have spent less time working on George's confidence and more time working on his upper body strength.
8. It's super-subtle, but the line "John F. Kennedy drive..." and the dad saying "Who the hell is John F. Kennedy?" is really stupid.
This line is really dumb for three reasons:
1. In 1955, JFK was already a Massachusetts senator.
2. Even if Lorraine's dad had no knowledge of Massachusetts senators, he would have known the name "Kennedy" because JFK's father, Joe Kennedy, was a massively famous businessman, and all dads know about massively famous businessmen.
3. Even if, somehow, someway, Lorraine's dad had never heard of any Kennedy, why would he ask who a street was named after? Do you know who every street in your town is named after? No. And you never, ever ask. Because people don't do that.
Special thanks to Dan Hopper for added complaints.