Miss Maudie’s gold bridgework twinkled. “You’re mighty dressed up, Miss Jean Louise,” she said, “Where are your britches today?”
“Under my dress.”

– Harper Lee

To Kill a Mockingbird, Chapter 24. Scout is a tomboy. At Aunt Alexandra’s missionary tea she is forced to wear a dress and feels uncomfortable and ill at ease. So she wears her trousers underneath the dress so that she can still feel more like herself.