Also could be used to describe others in the third person.
DJ Noodles: Hell yeah the boy's trying to party where we going?
Raul: Your mums hause.
DJ Noodles: Im finna beat the boy's ass running his mouth like that.
1) The way Homer Simpson refers to his son Bart as Bart is the only male child in the immediate family.
One may refer to any male child in a family as The Boy providing they are the only male child.
Doing so may seem a little insensitive so it is best avoided.
2) A person (male or female) who is "it". The best at whatever they are doing or just generally higher up than anyone else.
A person may believe they are The Boy when in fact they just frontin and are better described as The Bitch.
Psychiatrist: Homer, what do you see when you look at this card?
Homer: THE BOY!!!!!!!!!!!!!!!!!
Marge: If you just talk to him without mentioning our son Bart
Psychiatrist: You mean there really is a "Bart" ?!
Look at that guy over there just merkin everyone, he's the boy
Do you think you're the fuckin boy?
Rippee: I'm the boy me