Here's a joke that I used to find very funny, when I was a child:
Tire Salesman: "How'd you get that blow-out?"
Customer: "I ran over a milk bottle."
Tire Salesman: "Didn't you see it?"
Customer: "No - Damn kid had it under his jacket."
The problem if you tell it to kids these days is they just scratch their heads and ask, "What's a milk bottle?" It's just not funny if you have to explain.
I don't usually think of myself as all that old (but when I do, I'm sure I always whine about it here), but I do remember the day when we did not buy our dairy products in the market. Instead, they were delivered, fresh, to our door a couple of times each week by the milk man.
That used to be a funny joke too: saying somebody's kid looked like the milk man. Now, again, it draws blank stairs and mumblings of, "What's a milk man?"
You could replace "milk man" in that joke with "mail man", but who the hell knows what their mail man looks like anymore? Not to mention that the postal worker is now as likely to be a woman as a man.
This is why nothing is funny anymore, and the world is in such turmoil. Besides all the changes in terminology and delivery, we're also all lactose intollerant.