Son:"Daddy, I fell in love & want to date this awesome girl!"

Father: "That's great son. Who is she?"
Son: "It's Sandra, the neighbor's daughter"
Father: "Ohhh I wish you hadn't said that.
I have to tell u something son, but you must promise not to tell your mother.
Sandra is actually your sister.
"The boy is naturally bummed out, but a couple of months later ...
Son: "Daddy, I fell in love again n she is even hotter!"
Father: "That's great son. Who is she?"
Son: "It's Angela, the other neighbor's daughter."
Father: "Ohhhh I wish you hadn't said that.Angela is also your sister."
This went on couple of times and the son was so mad, he went straight to his mother crying.
Son:"Mum I am so mad at dad! I fell in love with six girls but I can't date any of them because dad is their father!"
The mother hugs him affectionately and says: "My love, you can date whoever you want. Don't listen to him He isn't your father."