Make up a story about how you had a gray hair and you went to pluck it out but your mother threw a fit because she believes in the myth about how if you pluck one gray hair, many more will grow.
"I was standing in front of my mother's bathroom mirror waiting for her to pick out a presentable tie for me to wear to some fancy dinner we were invited to. When looking at myself, I noticed a shine on the top of my head right where the hair met my forehead. I quickly realized it was a gray hair...."
Or maybe the old "If you go outside you'll catch a cold"
"It was freezing outside one winter day and my brother/sister and I wanted to go play in the snow. (if it doesn't snow where you live say you were on vacation) I had just taken a shower, and like most days I felt too lazy to attempt to dry out my hair.....Just as I was walking out the door my mother yelled at me..."
Just make the stuff up.
