[Kodak]

I don't go as far as most EM'ers, but I've encountered some people who seem to think that it's kind of silly.

Confidently state how practical your actions are. That's all there is to it. Point out that your actions benefit you, and are clearly in your favor. It helps if you remember that you have no need to justify your own actions, nor to convince others to imitate you. You're merely serving your own self interests (fuel economy), and allowing others to pursue theirs.