Ever since the Bush daughters got into trouble with the law for underage drinking, the President has lectured them constantly about the evils of alcohol. His daughters were tired of having the same conversation week after week, so they finally said, "Okay daddy, we understand about drinking already, but you've never talked about to us about sex."
Getting very upset, W. chided the twins: "Young ladies, we do not use that dirty four-letter word in our home!"