heh, I know the feeling. I now head those off at the pass. As sson as the deconstruction of my opnions starts, I say something like: "Hey, that's just my opinion. You do whatever you want." It usually cuts the crap out. She may explain why she wants to do what she wants, but at least, it's not adversarial any more. In your case: "honey, I think you should get a Honda anyway, because they tend to not leak oil all over your clean garage. That and I don't need to wear ear plugs when I'm on the back with you. But that's just my opinion - if you really want a Harley, go for it!"
The differentiation song:
All I want to do
Is be more like me
And be less like you
Linkin Park
