Old Wives' Tales

Growing up, there were many tales told to me by my elders that of course I now know are just that, tales. ...Although I must say I believed them with all my heart when I was but a child knee high. I will give you a few examples.
I was told never to swallow any seeds, be it from oranges, watermelon or other seedy fruits. Why? Because if I did, I can expect the seed to germinate and grow out of my head. Pretty dumb to believe huh? Another one is to make sure I finished every morsel on my plate, otherwise I will grow up and marry a person with lots of pimples on his face.
I realize that these tales are meant to teach us something. So now, with a child of my own, I wonder what I can come up with to teach him stuff. Should I tell him not to suck on his daddy's hairy legs unless he wants hair to sprout out of his tongue?
What about you, what did your parents tell you that you now know is just a fable?