I worked with a friend of mine up until a year or so ago. He was a Christian and seemed from comments that he made from time to time to not believe in evolution. In a casual conversation one day he was disparaging evolution, strongly implying that it was ridiculous, etc. I tried a new conversational tactic that I had developed just a year or so before this on him. I simply blurted out in response, "So you believe in a story with a talking snake and magic fruit." It had the effect I intended. It took him totally by surprise and he said that he had never heard anyone put it that way before to which I responded, "Well, that's exactly what it says!" I suspect that he could now see that it his beliefs could be made to appear absurd too. I am not saying that I converted him for I did not. But I did get him to pause and rethink his rhetoric. Unfortunately he left our company before I could debate him again.
The point is that sometimes you need to throw the more ridiculous aspects of Christianity back at them when they take that approach with you that your belief in naturalism is absurd. It certainly won't always work, but I am sure that many times you will be able to at least get them to pause and reflect on the absurdity of their own beliefs for a few seconds anyway.