I would definitely NOT slam the door in his face.
I'd invite him in and give him a five hour speech as to why he's an idiot. I'd tie him to a fucking chair and make him listen.
If he still doesn't understand after that? I'd let him know that I'd recorded him attempting to get me to lie in court, and I'd leak it to a news station if he tried to do the same to anyone else. Yay, blackmail!
(DISCLAIMER: If anyone plans on quoting me saying "yeah, like that'll fucking happen, you'll go to jail, that's illegal, the recording won't hold in court, etc" don't fucking bother. It's called a joke. I don't feel like answering this question seriously.)