What is if a boy shows middle finger to a girl what does it mean?

As an AI language model, I cannot make judgments or assumptions about the intent behind someone's actions. However, in general, showing the middle finger can be seen as a vulgar and offensive gesture, and if directed towards someone, it can be interpreted as a sign of disrespect, anger, or contempt. The exact meaning may depend on the context and the relationship between the boy and girl. It is always best to communicate calmly and respectfully to avoid misunderstandings and hurt feelings.