I went to my granddaughter's birthday party last Saturday. I sat next to and communicated with fundamentalist Christians. We actually got along and had a good time. Of course we never brought up politics or religion. My reputation as an outspoken atheist proceeds me,but I showed them that I can fun and engaging without jumping down their throats. I saw that in them too. We both also had enough reason to know that there is a time and place. This could lead to a later civil discussion about religion. Of course it may well not. But I think we showed each other that civility can occur in both csmps
Most of my relatives on my Dad's side are Pentecostal Christians who've been nothing but nice and helpful to me throughout my life. I'm sure they've heard the rumors about my beliefs (dating back to the 70's) and still they invite me to the family holiday dinners on the 4th, Thanksgiving and Christmas. So as long as I keep my religious opinions to myself and they don't start speaking in tongues and laying the hands on me, we're all cool.
I have been there so many times and, like you, am proud that I kept it cool. HOWEVER that is not the case when we go deep with someone. Superficial conversation is fine to pass time and chat it up but to hear someone's views straight up, that is another thing.