We all love to debate about religion, but where's the fun if we have to debate what other people actually believe instead of some ridiculous straw-man version? I therefore present to you the straw atheist and the straw Christian, based on screamingly inaccurate assertions that "everyone knows" to be true.
The straw atheist
Atheism is an intellectual monolith. All atheists believe in the aspects that you find most objectionable of the writings of Richard Dawkins, Friedrich Nietzsche, Karl Marx, and Ayn Rand (or, rather, what you think those people wrote). In particular, all atheists, without exception, are nihilists and moral relativists who worship science as their god and who think that there's nothing particularly wrong with adultery. It is therefore perfectly appropriate to put any atheist on the spot to defend any of those things.
Politically, all of atheism is the (circle whichever applies: Democratic, Communist, Libertarian) Party at non-prayer. Atheists claim to want to be left alone, but they're actually plotting to take over the United States Government and repeal the free-exercise clause. Atheists are particularly plotting to outlaw all Christian symbols, even on private property, and all public mention of Christmas.
Atheists are angry with God (and how that works is something that you will have to figure out for yourself) for not letting them fornicate and do drugs. They probably had something bad happen to them that made them even angrier with God.
Atheists are mostly either angsty teenagers or social-skills-challenged losers. The latter use atheism as cover for their inability to get laid.
Atheists are atheists because they have never been told about Jesus. Once they hear your superior arguments, they will immediately convert to Christianity.
The straw Christian
Christianity is a theological monolith. All Christians believe in the aspects that you find most objectionable of Catholicism, evangelical Protestantism, Pentecostalism, and Mormonism (or, rather, what you think those branches of Christianity teach). You needn't worry about Eastern Orthodoxy, since it doesn't exist. In particular, all Christians, without exception, take all of the following as necessary for salvation: young-earth creationism, transubstantiation, priestly celibacy, the use of priestly vestments, a rejection of everything not found in the King James Bible, and teetotalism. It is therefore perfectly appropriate to put any Christian on the spot to defend any of those things.
Politically, all of Christianity is the conservative wing of the Republican Party at prayer. Christians want to remove themselves from everything worldly, except when they're plotting to take over the United States Government and repeal the establishment clause. Christians all want certain passages of Leviticus written into secular law.
All Christians who are still Christians in adulthood are unintelligent, either because they have always been that way or because they did too many drugs before converting. Christians who somehow make it to good universities deconvert while there. They may pretend to remain in the faith to give themselves cover for their inability to get laid.
Christians hate not only gays and Democrats, but also people of different races, poor people, and the handicapped. Christians are superficially incredibly nice, but once they discover that you are not exactly like them, the knives come out.
Christians are Christians because they have never been told of any other options. Once they hear your superior arguments, they will immediately convert to your religion (or deconvert altogether if you are an atheist).