All Boys Were Cross Dressers

Notice anything strange about this clown?  He is wearing a French Pierrot outfit with a Charlie Chaplin Derby, an umbrella and a depressed Emmett Kelly expression.   A weird comic cross dresser
.

Which of course reminds me of men.

Until the late 19th or early 20th Centuries both boys and girls wore dresses.  Some of the little boys were given trousers by age two, but many had to wear their dresses until they were eight years old.

Hence the expression, "You run like a girl."