Recently there has been a mini-debate among atheists about whether their critique of religion should remain "civil" (i.e. polite).
Clearly they have never read the words of the Book of Proverbs about the most effective way of upsetting someone being to be nice to them. (“If your enemy is hungry give him bread to eat, And if he is
thirsty give him water to drink, for so you will heap coals of fire on
his head.” (Prov. 25:21,22))
Personally I find that I can offer trenchant criticism of the bits of Christianity that I dislike (penal substitution theology, homophobia, and the idea that other religions are wrong) without offending my Christian friends or making remarks that imply they are all stupid or malignant. Occasionally I get it wrong, and have upset moderate Christians by not being specific enough in my criticism, but for the most part, many Christians agree with my criticisms, or at least find them interesting.
Bigoted and extreme Christians like the odious and repellent Stephen Green do find my criticisms offensive - but he, and his nasty bigoted organisation, have put themselves beyond the pale of civilised discourse anyway. I really felt pleased that my views were deeply offensive to Stephen Green.
I do think that criticism is more effective, and more likely to be listened to, when it is backed up with reason and evidence, describes the situation accurately, and does not include ad hominem attacks. A lot of recent atheist attacks on religion have failed on one or more of these criteria. And conversely, a lot of recent Christian attacks on secularism and equality have dismally failed on one or more of these criteria.
Also, civilisation is founded on being civil. We don't settle arguments by barbaric means such as trial by ordeal, burning at the stake, and torture any more. Instead, the best means of demolishing your opponent's arguments are the well-placed witticism, the cogent argument, and sometimes, just ignoring them as irrelevant. If you really want to upset someone, just ignore them. As Oscar Wilde said, "The only thing worse than being talked about is not being talked about."