what are we supposed to say again when christians ask us where we get our morality?

[Cato]

It's not that easy. Some of us are compatibilists.

As in you believe in the compatibility of God’s pre-ordination and man’s will?

If you don't know what compatibilism is you should refrain from participating in discussions of morality that are more than surface deep.

Despite my previous answer, I don't really run around kicking people in the balls.

The typical way I handle this is to ask my interlocutor if believers are big on stoning to death disobedient children. After the obvious answer I then point out that the standard of good and evil for believers is also extra biblical. No amount of goal post shifting or obfuscation can avoid this conclusion.

You’ll have to be more specific.

You have this backward. I gave a concrete example. You must then be looking for something more general or abstract.

Believers don't follow all the moral edicts written in the Bible; therefore, the standard of good and evil is outside the Bible.