I'd heard this one before but it's still good for a laugh.
A first grade teacher explains to her class that she is a Yankees fan. She asks her students to raise their hands if they, too, are Yankees fans.
Everyone in the class raises their hand expect one little girl. The teacher looks at the girl with surprise and says, "Janie, why didn't you raise your hand?"
"Because I'm not a Yankees fan," she replied.
The teacher, still shocked, asked, "Well, if you are not a Yankees fan, then who are you a fan of?"
"I am a Red Sox fan, and proud of it," Janie replied.
The teacher could not believe her ears. "Janie, why pray tell are you a Red Sox fan?"
"Because my mom is a Red Sox fan, and my dad is Red Sox fan, so I'm a Red Sox fan too!"
"Well," said the teacher in a obviously annoyed tone, "That is no reason for you to be a Red Sox fan. You don't have to be just like your parents all of the time. What if your mom were a moron and your dad were a moron,
what would you be then?"
"Then," Janie smiled, "I'd be a Yankees fan."