A man and his son are driving in a car one day, when they get into a fatal accident. The man is killed instantly. The boy is knocked unconscious, but he is still alive. He is rushed to hospital, and will need immediate surgery. The doctor enters the emergency room, looks at the boy, and says...

"I can't operate on this boy, he is my son."

So, the question is, how is this possible? The answer is simple: the doctor is the boy's mother. This riddle has been told for a long time, to illustrate how common gender stereotypes are in our society. What's fun, is to tell this to closet feminists like my mother or sister, and watch them fail to get past the stereotype of thinking "doctor" implies "man".