They couldn't change a light bulb.
I once heard some people talking about tenants who had lived in their rental property.
"They were nice folks, but they couldn't do anything around the house. They couldn't change a light bulb."
I thought they were using a figure of speech. Turns out, the people came from a New York apartment building where if anything needed to be done, like a burned-out light bulb replaced, they called the super.
Reminds me of a story my brother once told me. Our family lived in Los Angeles. He was in Idaho on business and one of the people there said he really should come up in the spring because the fishing was terrific.
My brother said, "That sounds fun. I've never been fishing."
My brother said everyone in the room stopped and looked at him in silence like he was from another planet.