How to tell your daughter that she needs to wear a shirt

My daughter is at the age where she needs to start wearing a shirt, but she doesn't understand why. When I tell her to put one on she rolls her eyes and gives me that how-come-I-have-to-wear-a-shirt-when-my-brother-gets-to-go-topless-all-the-time look.

"I know it's a dumb rule but it's still a rule," I tell her. "And I promise that if you want to protest this law against girls showing their boobs when you're a grownup I will support you completely.  But for now, as long as you're MY responsibility, you're going to wear a shirt."

She grumbles and grabs a t-shirt.  As she pulls it on inspiration hits.

"You want to hear a secret?" I ask.