Going about this the wrong way.

If someone detests the good herb, they will always. Especially an adult. That is how they see it; they have their reasons, you have yours. It's a futile arguement and a trivial pursuit, he will not change his mind. Your best bet is to put it in the past and not bring up your weed habbit. Let it fade away. Don't bring it around them or their house, and just let it fade to black.

You're only making things messier.