A new car.

One day a mother and father were having sex and their son walked in. "What are you doing, the kid asked".Well, you wanted a brother, so we're making you one.The next day, the father walks outside and sees his son porking away on the family junker's tailpipe." Son...
what the hell are you doing!!!"And the son replied - "Mom said she wanted an new car, so I'm making her one!"