My parents aren't devout Christians - it's not the centre of their life, it's just something they do on Sunday and during bake sales - so telling them I'm an atheist wasn't a problem with them at all.
My fiance's Catholic family, however, is another story. His father in particular is a devout Catholic. At one point he wasn't even going to walk his daughter down the aisle because she lived with her fiance before they got married, but he's loosened up a little over the years. He helped us move our stuff here and will visit us, but will seldom accept food or drink in our house.
So how I came out to my fiance's family - I got really drunk at their house and blurted it out. LOL! My fiance's dad started pouring everyone whiskey and I have a very low tolerance for alcohol, so it went right to my head after the second drink. They began pressuring us about having a Catholic wedding, and after our polite, non-committal answers didn't cause them to back the hell off, I eventually blurted out, "I'm an atheist, so no, that's not happening." LOL! I'm not sure his dad heard me or not (he was in the kitchen and is hard of hearing), but his half-brothers and step-mother definitely heard it.
Strangely enough, since then my fiance has been pretty open about his disdain for religion in his family - to everyone except his father. I guess he thinks that his dad is up there in years and it just isn't worth 'putting that on him.' The way I see it, they're putting their religion on US, so I don't know why it has to be this shameful little secret. I don't see why we can't just...be us, you know?
The next time they start pushing the Catholic wedding stuff on us, I'll be tempted to say, "Well sorry, but I found a sweet and fabulous gay Justice of the Peace who is an ex-Catholic priest and is now a Hawaiian shaman who does secular weddings. Oh yeah, and we're eloping because it's something I've always wanted to do."
Ahh, if only I had the courage to say what I really want to say instead of censoring myself all the time. LOL! I'd probably have no friends.