I thought more about this this morning and I wanted to write out a bit more thorough response, just in case I didn't explain things very well in the teaching I did on atheism, so that everyone reading can hopefully understand how to give simple responses to give to atheists.
Atheists love to immediately take control of a conversation, and that's because they're afraid. Do not let them scare you or intimidate you with their scoffing, hateful attitudes because inwardly, they are scared to death. Their worldview has no basis for truth and knowledge, they don't know what's going on, where they are going, or what they ought to do; they are swimming in an ocean of uncertainty with a ridiculously circular worldview, and they outwardly show their fear by their anger. So please keep that in mind.
I don't care what an atheist wants to approach me with because I immediately tell them that I'm surprised they would say that since they have a religious worldview (and yes, atheism is religious) that can't account for logic, reason, science, math, morals, or anything else in this world. I prefer to tell them that I've researched some really silly religions (e.g. Mormonism, Scientology, Catholicism, etc), and atheism is the most ridiculous among them because they can't even justify that evil exists in their own universe.
That's how you take control of the conversation; you all need to go on the offensive because these atheist men and women are held accountable to the Living God who they know exists, but they hold the truth in unrighteousness.
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;
-Rom 1:18You don't have to be mean, but be firm. You have the Christian worldview that can justify truth; they have a worldview that can't. So move it there: Tell me atheist, how can you justify evil exists in an atheist universe?
There's only a handful of things they will try, but I explain it in more detail in the atheist teaching I did:
http://www.creationliberty.com/articles/atheism.phpFor example, they commonly try to appeal to majority opinion. Majority opinion is a logical fallacy, and atheists are obsessed with "logic" so they get upset when you point this out to them. They'll say, "We have laws" or "Society gets together and decides" or "Most people feel like" -- that's all logical fallacy.
Speaking of feelings, that's also called "Appeal to Emotion," which is what people do when they put their feelings in place of facts. I prefer to bring up the subject of raping a woman to them, because in our society right now, rape is a very grievous crime, so I ask them to justify why rape is wrong. It's hilarious where they go from there.
Usually, what every atheist ends up boiling down to is that it is wrong to "harm" someone else. To that, I ask them, "Why is it wrong to harm someone else?" Every answer they give goes back to Appeal to Emotion, Appeal to Majority, Appeal to Nature (which is where they give the example of the animal kingdom)--all of which demonstrate this point, and here's what you end up telling them: "You just showed everyone that the foundation of atheism is in logical fallacy and hopeless circular reasoning."
Then you can into the Bible and show them their complete hypocrisy. They are out there trying to say they are "good" people, first of all: Make them prove it. Once they attempt it and fail completely, trying to talk about that it's "bad to harm people," and they can't give a justification for it without diving into logical fallacies, then you show them why it's wrong to harm other people... you go right into Matthew 7, which I have said is one of my most used chapters in the Bible:
Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets.
-Mat 7:12This is why they deny the truth. They hold the truth in unrighteousness. They believe what Jesus taught is the truth, but they deny Him because they are wicked in their hearts, and need to repent of their sins. The fact that they attempt to justify "good" or "evil" in the world, is bearing witness of the truth of God in their hearts:
Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;
-Rom 2:15They bear witness of the truth by the very fact that they stop to speak to you at all. The second they walk up to you and open their mouths, they have given witness of the truth of God's Word because if they truly believed in atheism, they wouldn't get out of bed in the morning because there would be no reason to do so.