This is about an old girlfriend from my college days. She was REALLY bad about tailgating and every time she drove, I spent half of it trying to push my foot through the passenger side floorboard and fearing for my life. Nothing I said got her to stop doing it.
One day we were on our way to her dad's office (where I occasionally worked during breaks and summers). She about scared me to death on the way there and we got into an argument about it. He sort of refereed the fight without passing judgement, but after she left he said, "Son, we both know you're right and I love my daughter, but you need to get it through your head that there's NO SUCH THING as a logical woman and you're not going to change her driving until she hits someone."
A month later he stepped into my office and said, "Come on, we're going to the ER. She rear ended somebody. She's OK, but she's got a bloody nose and a busted lip. I assume I don't need to explain to you why you shouldn't say, 'I told you so' when we get there, do I?"