If only he knew that in alienating his sister, he is jeopardizing his prospects of someday learning from her absolutely essential things about the world of girls and women, to which he cannot hope to gain access by any other means. Sadly, this probably won't impress him much now.
A boy who grows up without a sister is just plain doomed. I wish I could explain this to your son. It is perhaps the single greatest life lesson I have learned.