It's interesting how there seems to be a double standard held by certain people in this respect. For instance: I've heard many religious people say that gay couples holding hands on the street is "shoving their sexuality in our faces". But literally shoving Bibles in people's faces in the street is somehow ok for those same people. Interesting.
I think it's fair to match your response to the person's attitude: if they are discreet about their religion (don't convert people, maybe only mention it if asked) be discreet about your different belief/lack of it. If they're invasive about it, you get to be a bit rude. Now I don't actually do this irl most of the time because I do like to be nice if I can (shocking, I know), but I don't blame people who do.
Hmm, I don't really agree that gay couples holding hands is "shoving sexuality into our faces". Maybe I may not agree with homosexuality, but unless it starts to be invasive (like for example saying bad stuff about het people or maybe being rude and pressing when someone says they're not comfortable about open displays of homosexuality, but I honestly have yet to personally talk with any of the two kinds). When "shoving Bibles into people's faces", I don't think anyone can be forceful and rude (because if they are, they are being a very bad example of Christianity).
Also, if by "invasive" you mean converting, well, just saying that we truly intend for the best. No one is forcing you, but I personally have discovered a great joy in God, so I naturally would like to share it with other people. If someone is rude because of that, that would hurt me. And yes, the same could happen with gay people. If someone is rude they will get hurt, because they are people. I think respect is the most important thing, and trying to see the intentions behind people's actions is fundamental.
Then again, this is beginning to tread into uncomfortable territory I think, so it may be safer to change discussion?