I'm just going to steal the response I read years ago.
"I possess a device, in my pocket, that is capable of accessing the entirety of information known to man. I use it to look at pictures of cats and get into arguments with strangers."
I'm going to go on a different angle on this one and say that we are much tougher on sexual harassment. I feel like a lot of people from the 1950s who have grown up on pulp sci-fi like Flash Gordon could accept a lot of modern technology and the internet as basically just magic. To be fair is how a lot of modern people also accept it. But I don't think they would be able to process the move towards egalitarianism that we have taken.
That is not to say that modern society is egalitarian only that we have made good strides in achieving that aim.
Edit: Turns out Gordon is from the '70s, but other pulp sci-fi exist so my statement stands.
Things they considered morally fine (smoking, dropping litter, 40 year olds dating 16 year olds) is morally reprehensible, while things they thought were morally wrong or even outlawed are totally acceptable (homosexually, porn, divorce).
We walk around with a little rectangle in our pocket that gives us access to the sum total of human knowledge, but we mostly use it for looking at funny captioned pictures, the same pictures over and over just with different captions.
It's called a phone but no one ever uses it as one.
Most difficult imho would be to explain why we haven't advanced any further. If the person is 50 in 1950 he started with horse carriages and saw development to intercontinental bombers, rockets etc. The landing on moon would astonish him, advances in medical sciences and computing too but he probably would ask: "And what are you using that neat little gadgets for?"
nature and resources are not infinite.
you are responsible for your actions no matter how terribly hard your childhood was. you cant buy a house for a years loan. we are all fucked.
A significant chunk of Americans support Russia over their own country and are actually opposed to the US providing aid to a country being attacked by Russia. I mean, I guess they had the Red Scare, but this is more Americans opposed to Left-leaning politics who support Russia's authoritarianism.
How nothing got better and people like killing children in the school system as sport. Oh, and ask this person what pronouns they want for their identity.
Probably how we went to the moon and then later successfully sent a rover to Mars to study and take pictures. It's something I can't really explain on a technical level but it happened
That we've been to the moon and back, and that they can casually toss into their pockets a device with enough "thinking" power to do the necessary math for the task and then some.
And that we still can't make nylon stockings that don't "run," but that nobody cares because we don't wear them anymore.
how old were they in the 50s and how old are they now? That's probably the crucial thing to know. 70 year old was born in the 1880s and probably would have difficult time to understand much of the current society. 15 year old would probably learn quickly new technology and societal norms. If they'd be middle aged or a bit older man, they'd probably be quite uneducated and would probably have difficult time socially to adapt modern society, where you can't casually sexually harass women and where you don't get job simply by walking to work place without a college degree.
If it was the early 1950's, then: Black people and white people can use the same facilities. There aren't "black bathrooms" and "white bathrooms." There aren't separate water fountains depending on the color of your skin.
I think where technology is in general would be really difficult to grasp. Imagine telling someone you can instantly get a hold of all of your family members and friends wherever they are. Or that They could just press and button and get instant, overwhelming amounts of entertainment or up-to-date information from across the world. Imagine trying to explain how airpods work to a person that has never experienced active noise canceling. Or rule 196, or rule 34 for that matter.
That we gained the capacity to send people to the moon only to use it for winning a political dick-measuring contest in the 60s and not do anything with it again for 50 years