No one can be good all of the time. And, more interestingly, being good can sometimes be bad. For instance, sometimes when visiting relatives or friends, they may use paper plates, paper towels (in the bathroom even!), paper napkins, etc. But, I would be a horrible ass if I were to a) state out loud to the people who are giving me a free place to stay and providing me with delicious meals that paper plates are wasteful or b) refuse to use the paper plates and throw an environmental hissy-fit. Both of those options are absolutely inexcusable in my book.
That's not to say that I wouldn't have made a scene ten years ago or last month at my mom's house (because she expects it from me.) I've been there. I've railed against American excess and wastefulness. I've loudly lamented the disposable, consumer society we live in. And, really, all that resulted from my loud protests was me looking like an ungrateful punk.
In my experience, the only way to truly be a good environmental example is to do just that. I try to do the best I can in my own life and, hopefully, at some point, some of it rubs off on other people. I'm still going to speak my mind about excess and wastefulness like the goody-goody that I am, but I'll keep my audience in mind and mostly preach to the choir or to small children who can be easily brainwashed.