Do you know of anything your grandparents said to you when you were young and now think of how stupid that was?

When stupidity is harmless it can be fun. My brother in law said a month back that fish can live a long time out of water. He saw I was going to call him on it and he doubled down. Luckily, I straightened that out. I made sure the kids knew. We can teach our kids some crazy shit if we believe it ourselves. My grandma was insistent that we'd get worms crawling out of our butts if we ate too much candy. That wasn't a grandma saying either to get us to stop. She truly believed it.

Do you know of anything your grandparents said to you when you were young and now think of how stupid that was?
Do you know of anything your grandparents said to you when you were young and now think of how stupid that was?
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