Here’s a nice means of nailing an atheist’s hide to the wall and having some fun at the same time. When one goes on the customary “religion is responsible for most of the wars in history” rant, instead of arguing with them, agree wholeheartedly and state your admiration of their brave, contrarian support for Mel Gibson’s idea that the Jews are responsible for all the war in the world.
This, of course, will lead to an immediate and vehement denial that they meant to blame it on the Jews. So, ask them what religion they had in mind, if they weren’t thinking of Jews. These days, most atheists will say Islam, and some will say Christianity. In response, ask them who started the Roman-Jewish wars, the Muslims or the Christians. (The Jews started all three, by the way, as all three were revolts against Rome. Can’t say I blame them either.)
If your poor atheist is slow enough, you can have some fun when they try to blame it on the Romans in order to avoid being accused of anti-semitism. If not, you can ask them who started the wars that Sun Tzu was writing about, the Muslims, the Christians or the Jews. At this point, they’ll probably admit that they have no idea what they’re talking about, unless they’re particularly stubborn, in which case they’ll bring up the Crusades, the Thirty Years War and the Spanish Inquisition.
If you can’t handle it from that point, you haven’t been paying attention here.
Another, similarly amusing tactic can be to ask an atheist who the greatest general in history was, then ask what religion Alexander the Great, Julius Caesar, Sun Tzu or Genghis Khan subscribed to. Don’t get me wrong, there are plenty of intelligent and historically knowledgeable atheists out there, it’s just that such a wildly stupid comment is a sure sign that you’re not dealing with one of them.