When one of my sisters was little, we were in the car driving to church. We lived about 45 minutes from church, so that gave us a lot of time to talk and play on the way there and back. My sister piped up from the back that she had a "joke".
"How do you drive a car without any wheels?"
My mom, whom the question was directed towards, said, "I don't know. How?"
And then my sister burst into laughter. After all, it was a joke.
And then another joke: "How do you turn on a faucet without any handles?"
"I don't know. How?"
"You don't!" (and of course, more laughter!)
Soon we were all in on the joking. And you know, of course, that there are "knock-knock" jokes, "blonde" jokes, and now (for our family), "you don't" jokes.
These "jokes" lived on in our family. When you couldn't do something, it was a "you don't joke".
When Kevin and I were on our honeymoon, the restaurant we had reservations for was on one side of the freeway, and we were on the other side. My new husband was trying to figure out how to get to the other side of the freeway, and asked, "but how do you get over there?" Not that he really expected an answer! I'm the last person he'd ask for directions from, since I'm so directionally challenged! But I answered his question, "it's a 'you don't joke'!" Since this was the first time he'd ever heard of such jokes, I had a little explaining to do!
My mom was able to come help me when I had our daughter, and she was in the bathroom cleaning. She asked me how I cleaned under/beside the claw foot tub. I called back, "It's a 'you don't joke'!" No explaining necessary!
Most families have their own words or catch phrases. It's a fun thing to have as a family - a word or phrase that is just as unique as your family is!