Militant atheism gets a bad wrap.
I'm just about as anti-religious as you can get. I'm completely opposed to virtually all forms of religious belief. I think living by faith is a horrible thing that is destructive to humanity and that all people should live evidence-based lives using critical thinking, science, reason, and a little skepticism.
That being said there should be some etiquette involved when opposing religious belief. Militant atheism should be like a switch that is turned off most of the time and only turned on when faced with a theist of the militant type or when opposing a law or rule that discriminates against non-believers. Atheists should not ever be standing on corners with blow-horns, ranting about there not being a god to annoyed passers-by. We should not be confronting believers with those in-your-face tactics that theists are so fond of. We should however, be open about our non-belief but in the right way.
So I've thought of a few suggestions on rules of etiquette when it comes to expressing non-belief publicly. Although this is a "Gentleman's" guide I do not intend this to be from a male's perspective only. These suggestions are gender-neutral (I just liked the way Gentleman's Guide sounded).
1. When a theist publicly expresses their religious beliefs to you, their beliefs immediately become fare-game for criticism and ridicule. The moment beliefs are forced onto you [or you are forced to acknowledge them]*, the atheist has every right to put those religious beliefs down, even if it is harsh. However, chose your reaction wisely. In professional environments it may not be wise to let the anti-theist in you out unrestrained. Start with a more casual approach and match the theist's demeanor. If he/she is being loud, rude and obnoxious about their faith, be loud, rude and obnoxious back. Depending on the environment however, you may want to restrain yourself.
2. With friends it is OK to initiate conversations dealing with religion and faith. Every friendship is different, so only you will know when and with whom it will be appropriate to bring up issues like religion and atheism. I've lost a few friends over my openness on atheism so tread cautiously and use your best judgement. Friends however, offer some of the best opportunities to have deep intellectual discussions on religion and atheism, so go for it.
3. With strangers or acquaintances initiating conversations about religion/faith/atheism is fine but it should be done so from a very cautious and friendly manner. Then depending on how far that person is willing to go with the conversation should determine your tone. It is rude to come at strangers with an openly hostile, anti-theist attitude. Leave that for the religious fanatics and rise above such pathetic tactics.
4. It is preferred to be open about your atheism when friends/family/acquaintances/co-workers initiate conversations about faith. Being open about atheism will help people who aren't used to dealing with atheists realize that we're by and large just normal people. However, for some atheists who might live in hostile environments to anyone lacking religious belief, it might be preferred if you keep your atheism low-key. This is a very hard subject, and everyone's situation may be different.
5. When it comes to the internet, the blogosphere, social networking sites and forums be as anti-theistic and confrontational as you'd like - that's what the internet's for. But, since you will be connected to your friends/family/acquaintances/co-workers on the internet, use the same precautions you would when exposing your antipathy towards religious belief in person.
6. Definitely join/support atheist and secular organizations that seek to better the playing field for non-believers. Join debate clubs, protest absurd violations of secularism, stand for political causes you are passionate for. The world needs confrontation. That's how change is made. If you are passionate about your atheism, do wear it on your sleeve but take the advice in number 3 above to express your atheism in a friendly manner where your level of militantism is handled maturely.
7. If you feel yourself being discriminated against because of your atheism at work, school or any other professional environment, speak out about it and make it known. Secularists have the upper hand today when it comes to discrimination and we can win many battles. Gone are the days that atheists can be openly discriminated against and this is because atheists fought to make themselves heard.
8. Do not feel sorry for criticizing someone's religious beliefs who deserves it. Enjoy putting their faith in its place. It's one of the greatest feelings any atheist can ever have. When dealing with a loud irrational fundamentalists theist, ridicule their beliefs without mercy and try to make them feel as stupid as possible for what they believe in. And if you've got an audience on your side, instigate them into joining you in the ridicule.
9. When it comes to dating/relationships it is also highly preferred to be open about your atheism. This allows you to honestly be yourself to your partner, and it's often a great conversation starter. It is best however to talk about these things before you start dating someone seriously, but that is not always the case. Is it moral to lie to someone about your religious beliefs in order to have sex with them? Yes. If a person will only have sex with you if they think you are religious, they are violating their own religious beliefs since virtually all religions forbid premarital sex. Therefore, they are hypocrites and liars and there is nothing wrong with lying to liars - so long as no one gets hurt badly.
10. Friendly theists who keep their religious beliefs to themselves should be respected as anyone else should. I have many friends who technically believe in god but who keep their beliefs to themselves. It's OK to occasionally challenge them but just don't do it too often to the point of becoming annoying. When it comes to family/acquaintances/co-workers who believe in god but who keep their religion to themselves, for the most part, let them be. They're not bugging you with their beliefs and you shouldn't be bugging them with yours. If you know they are open to conversations about religion, then by all means engage respectfully. But if they are not, then don't force it upon them. With family this could be violated depending on the relationship.
Those are all I can think of for now, as more come up I will add them here or tune them into a new post. These rules of etiquette should make militant atheism a reasonable stance and provide us who are opposed to religion with a framework to do so in a way that is not as equally annoying as the fundamentalists who shout like lunatics about their fairy-tale beliefs. If you have any advice/suggestions feel free to add them.
* Edit, September 5, 2014