No joke

I don't tell jokes in front of mom, because we get stuck at the first line with 'why' questions. Example:

A.: A man walked into a bar.
Mom: What man?
A.: A man.
Mom: Why'd he walk into the bar?
A.: It doesn't matter, mom.
Mom: It matters to me! I can't understand the joke without context.

But what I told over dinner wasn't a joke; it was just a story, not even. I thought of it because we were talking about things (i.e. edible plants) growing out of control.

A.: My friend was telling me that where her mom lives, in a small town in Minnesota, you never leave your car doors unlocked when you go to church. Otherwise, you come back and your car's full of rhubarb.
Mom: What? Why?
A.: Because there's so much rhubarb growing--
Mom: It grows right into the car?
A.: Um, no.
Dad: People give it away. People who grow it stick it in your car.
Mom: Their town doesn't pick up brush?
Dad: People don't want to waste it. They want to give it away to people who might use it.
Mom: I don't get it.

This went on for another round of explanation. Mom 'got it,' but still didn't get it. I.e. I just thought it was cute--it's not like in DC or Boston, 'don't forget to lock your car' is generally followed by 'or else it'll be full of rhubarb when you get back.' But once you have to over-explain it (to an engineer), it kind of loses its charm. Dad's an engineer, too, but he's less of an engineer in that way.