My girlfriend called me wilfully ignorant the other day. I told her that firstly I didn't know what that meant, and that, secondly, I could not be bothered to find out either.
I have a brother who's a Chemical Engineer and tends to live in his own little world.
I've called him a militant apathetic, with the attitude: "I don't care, I don't want to know, and if you try to tell me, I may hit you."
Well, actually he's a sweetheart and a great guy, even if he is sometimes kind of out there.
The other way I explain him is to say he's the kind of guy who might walk into a research lab wearing a lab coat with a sandwich in one pocket and a formaldeheyded frog in the other, and about 3 PM he could pull the sandwich out of his pocket and say "That's funny, I distinctly remember eating lunch."