Sam asks Mr Dobbs who Lil" Mac D is, and he replies he assumes it's his son James and that kids don't go by they given names anymore, it always lil" this and Doggy that. Sam is played by LL Cool J (Ladies Love Cool James) whose actual name is James Todd Smith. The nickname was given to him by his friend Mikey D.
Mr Dobbs tell Sam that kids don't use their real names, "it's all Lil this and Doggy that."
As one of the fathers of rap, LL Cool J and his peers are largely responsible for this phenomena.