Does Christian etiquette say you must fart everytime the preacher condemns an Atheist?

No that is upsurd!!!! And a preacher would ask his congregation to pray for atheist and that They come to know Jesus as their Saviour before they leave this world!!!!!! Not condemn them!

Come to him, to that living stone, rejected by men but in God's sight chosen and precious; and like living stones be yourselves built into a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ. For it stands in scripture: "Behold, I am laying in Zion a stone, a cornerstone chosen and precious, and he who believes in him will not be put to shame." To you therefore who believe, he is precious, but for those who do not believe, "The very stone which the builders rejected has become the head of the corner," and "A stone that will make men stumble, a rock that will make them fall"; for they stumble because they disobey the word, as they were destined to do. But you are a chosen race, a royal priesthood, a holy nation, God's own people, that you may declare the wonderful deeds of him who called you out of darkness into his marvelous light.