This is where I came in.

When I was a kid movies were always double features plus cartoons.

Does the term, double feature even mean anything to you? When did they stop showing double features I wonder? We would actually sit through some movie like Strangers on a Train and then a couple of cartoons like Tom and Jerry or the Road Runner (my personal favorite) and then sit through another movie, say, Roy Rogers in Pals of the Golden West.
Incidentally, Trigger, Roy's Horse got higher billing than Roy's wife Dale Evans in that one. That Roy. Seemed to like his horse better'n his wife.

You could enter the movie at any point. They didn't clear out the theater between showings. Didn't bring up the lights, just kept looping the films over and over. Often folks came in during the middle of a show. They watched whatever was left of the movie, then whatever came next and so on. Then the first show, the one that was playing when they entered, came on again and they would watch that until they got to the point where they had entered. Then they would get up and leave, saying, "This is where I came in."

But people use the expression "This is where I came in," now. Do they know how it started?

We speak of "dial tone." But no one actually has a phone with dials on it anymore. We dial up someone. Only we actually push buttons. Do kids understand that word?

People refer to "A catch 22," but do they know what that was originally? Catch-22 originated from a 1961 novel by Joseph Heller, where one bureaucratic regulation is dependent on another, which in turn is dependent on the first. I say things like, "you can't get there from here." I don't know where that came from.

Even kids say that they are going to "hit the hay." They probably don't know that mattresses used to be stuffed with hay or straw, so that's how "hit the hay" came to mean "go to bed."

Did you know that the term "deadline" originated in the American Civil War, where a prisoner would be shot if they crossed a line around the prison or prison camp? I didn't. Seems harsh. I didn't realize that the term "brownie points" came from Girl Scouts either! Brownie G.S. had a point system that gave girls points for achievement. The term was first used in World War II when soldiers acted silly or kid-like.

I did guess that "Close but no cigar" came from the fact that old carnivals gave out cigars as prizes. 'Course now it just means to come close to achieving your goal, but failing. People don't think of carnival prizes when they use that phrase.

Sometimes families have there own sayings. When I was a kid and I said in front of my mother, "I had somethin' to say, but I forgot it." My Mama would say, "Well, I guess it wasn't very important then." I guess her theory was that you wouldn't forget something like the house was on fire. I would say that to my kids too after I grew up.

One evening over thirty years ago at the dinner table, daughter dddragon said that she had forgotten what she was going to say, and I repeated my mother's line. Immediately 3D said, "Oh! Now I remember! I'm radioactive!" That became a family tradition.

Does your family have some private idiomatic expressions? Feel like sharing them?