Boys and girls

Amanda Gardener was eighteen. Her parents decided to have her birthday party in a hotel. About two hundred people came to the party.
An old woman was staying in the hotel. She heard the music and came into the party room. The young boys and girls were dancing in the middle of the room. The old lady sat down and watched. Then she said,
"When I was young, parties were different. It was very easy to tell who was a boy and who was a girl. Today it is very difficult to tell who is a boy and who is a girl.”
The person sitting next to her said nothing. The old lady continued,
"When I was young, boys wore trousers and girls wore dresses. Look at that girl over there. She's wearing boy's jeans."
The person sitting next to her said nothing. The old lady continued,
"When I was young, boys had short hair and girls had long hair, so it was very easy to tell who was a boy and who was a girl. That girl's hair is very short. It is a boy's haircut."
The person sitting next to her said nothing. Then the old lady said,
"Do you think she is a boy or a girl? It is very difficult to tell, isn't it?"
The person sitting next to her said,
"No. It is very easy for me because that girl is my daughter.”
The old lady was very embarrassed and she said,
"Oh dear. I'm sorry. I didn't know you were her father."
The person sitting next to her replied,
“I'm not her father. I'm her mother.”