Authenticity is key to a happy and healthy life. Always be yourself; don't pretend to be something that you're not.
Thankfully, I don't. I didn't actually pretend to be Christian after I burned off my faith. I was just never approached about it or asked a direct question. I said what I thought on whatever subject and they just never brought it down to asking about that.
I don't pretend, but depending on the group of people I'm around, & the reason I'm a there. People can believe what they want, & my Beliefs are my own, & I don't always Share them, so to remain focused on the moment.
I have a direct question policy. I keep my lack of religion quiet unless asked directly. I generally scoot around the most common question "What church do you go to?" with "I don't have a church. I've never found one that works." Then they, of course, plug their own church; I reply "thanks, no thanks." and go about my day.
I normally just go with the flow if it is in a private household and this is what they believe or normally do. However my last job was working for a church and although I loved the work I often felt uncomfortable when it was suggested I attend church sessions. I felt that if I respect what they believe they should also respect my beliefs.
Hell no! I don't care one way or the other.. if they don't like too bad, so sad!
I've learned to be me....and if they can't handle it fuck em. I live in the Bible belt and you can't throw a stick without hitting some church, synagogue, mosque or house of worship around here, but I push back when they start in with all their mumbo-jumbo crap.