The Tower of Babel
No, really. How do you justify this story? It makes no f-ing sense at all. Basically:
1. Back then, we were all one civilization and spoke the same language. (false)
2. We were planning to build a huge tower that would reach the heavens (impossible with bronze age tech, even more impossible since all but the most crazy fundies would admit that heaven is not in the clouds)
3. God got angry with this. (why? a challenge to his power? He's all powerful! Us getting too arrogant? We're working together to accomplish something, and he didn't shoot down Apollo!)
4. So he decided to knock the tower down and changed all of our languages. (why? Surely he wasn't afraid of a bronze age civilization, was he? And doesn't this interfere with our free will, that is, changing our minds so we forget our language and magically speak another, something so important God felt that making us perfect was not worth giving up our free will?)