There's a few more than 12 here, but they're grouped with others of similar ideas. (If you can answer all these well, you just might be able to convert someone!)

1. When God said, "Go forth and multiply" did he not understand the problems that are caused by exponential population growth, or did he just choose not to tell us?

2. If human's were made in God's image, then does God have any of the following: nose, teeth, lungs, nipples, penis? And what would he use them for? What color is his skin?

3. When people of other faiths have near death experiences, why do they meet their own religious figures and never meet Jesus?

4. Most Christians rely on modern miracles to justify their faith. The favorite is Fatima. Why were there no first hand accounts reported at the time - only to appear later - not even by the media which had gathered to observe, and why did the three secrets supposedly told by Mary, never before mentioned, suddenly appear in 1942, AFTER the events 'predicted' in the first two had actually occurred?

5. How is it possible that Mary was a virgin at the time of Jesus birth when Jesus had two older brothers?

6. Why is it important to believe in/worship your God? For example:
- Why must people convert to Christianity, so much so that when the Church has sufficient power they will kill or torture those who won't?
- Why does your God need to be worshipped at all?
- why must you fear your all-good, loving God?

7. Why did God give you freedom of choice to choose only that which he wants you to choose or be punished?

8. When a child dies from birth complications, birth defects, disease or starvation, does God say 'Whoops!'

9. Why don't you follow the other religions? 5 billion people on this planet think your belief is incorrect. The odds are against you being right, so why would you be right instead of them?

10. Can you explain the existence of dinosaurs and neanderthals? Humans never interacted with dinosaurs or there'd be evidence. If God made all the animals for humans, then what's the point of animals that humans never encountered? If we are indeed made in God's image, then were the very similar looking neanderthals a mistake?

11. Why was not a single mention or word EVER written about Jesus by anyone who was alive at any time during Jesus' supposed life-time?

12. Aren't you worried that you may be worshipping the wrong God? The real one may be very displeased with your false idol.