When I'm explaining my dietary choices in following paleo (only when solicited), I have found that people's default, when they decide it's too hard to not eat bread (duh), is "well.....everything in moderation." They shrug, the conversation ends, and they walk away feeling like well-balanced individuals......while I'm the healthy one. :)
What can I say to them that will not be nasty or snarky, but will challenge them? I want to get people to think more about what they put into their bodies, or even to come back later for more discussion. The last thing I want to do is turn them off by acting like a snotty, know-it-all a-hole.