Christians why do you agree with Mike Huckabee that Atheists are Narcissistic?

I don't agree with him in that. And narcissism is more than simply "having a little bit of confidence in yourself." Actually, narcissism is considered a personality disorder. Now, to avoid offending anyone, I think the "narcissism" that you're referring to is not actually NPD, it's simply believing in yourself and being confident in yourself. I think you'll find that there are people from any cultural group or social group that have this confidence in themselves.