Personally I try to avoid comments to theists like "Your religion is HELP I AM TRAPPED IN 2006 PLEASE SEND A TIME MACHINE" or "God is imaginary" because frankly it puts me on the same level as the theists that systematically root out and destroyed my predecessors - those who questioned or rejected belief.
What I do try to aim for is discussion, debate, questioning and an educational experience from speaking with theists. Make no mistake, there are many theists more intelligent than little old me but I like to hear the reasoning behind some of the beliefs held by these individuals and to question, question and question some more. The only way to really change things is to do things like this on a local level and to admit that you won't win over most minds.
Sure, some people are close minded (or outright lunatics) because they often fear being honest about their practices (God is watching afterall) but let them fire the first volley, let them hang themselves with the nooses of manifested hatred they can't help but create and let them show those on the fence just how vile they can be when exorcised from the body of 'love, compassion and goodwill'.