When I was in elementary school, I remember seeing posters, ads, etc. on the walls of my classrooms using a sort of descriptive language that didn't make much sense to me at the time. I accepted it, as I did most things of that sort, because "grown-ups made it, and they're smarter than me, so there must be a reason." I was reminded of these phrases recently and realized they were, indeed, stupid.
"Make no bones about it!" - picture of a skeleton doing something
"Bone up on your reading!" - picture of skeleton reading
"Have a whale of a good time!" - picture of whale
As a kid, I had no idea that to "make bones," "bone up," or "have a whale" were real phrases that meant something beyond a reference to the picture on the poster. Nobody I knew used them, kid or adult. I thought the people designing these things just had a theme like Halloween or whales and made them up. If they wanted a monkey on it, they would just say, "Have a monkey of a good time!" Years later, I discovered that they were actual figures of speech, but I still don't know anyone who uses them. Thus, I conclude that the people who made these things for kids were stupid, because no kid uses or even knows about those phrases, so the puns aren't merely terrible, they're incomprehensible to their target audience.
Can anyone think of some others I'm forgetting?