Since most of the talking points of Christians are the hope of proving the existence of God, or at least a god, I give you the hypothetical that a god stepped on my foot and greeted me.
First off, I still would not believe it was a god. There's just no way of actually knowing that what stepped on my foot and greeted me was what people would describe as a god. Even if they looked mystical and could perform miraculous tasks, I would only give credit to it's manipulation of physical laws, not supernatural godliness. But let's just say that I thought it was a god.
1) There is nothing to say that this god is good. Certainly, there are numerous passages in the Bible where the god committed or supported genocide, rape, and other acts against humanity. And I refuse, and I do not believe, that you can separate the OT with the NT. Both are Christian scriptures. Both are used in support of Christianity. Therefore Christians cannot ignore the OT, no matter how much they'd like to. I will give them, out of pity, to say that "God grindeth slow, but exceedingly fine", but this would only be an explanation, not an excuse. The god described in the OT is the same god described in the NT, according to Christianity. I also cannot accept a god who makes the Ten Commandments (or any commandment over morality) as absolute rules. There are way too many contradicting situations, and there are way too many exceptions to the commands, like being asked by Nazis where I'm hiding Jews and being forced to tell the truth according to the Ten Commandments. So the Christian god is in no way defined as good in my book.
2) I don't need a god. There's nothing I would benefit from believing in a deity. It doesn't help me understand the universe I live in. My life would remain the same. Christian's will try to say that there will be a point in my life where hardships will befall on me, and I'll need support - specifically Christian support. But I counter-argue that you cannot guarantee that this will happen, and even if it did, I would prefer that I would get my own way out of it or see a therapist - learning most from the former – and thus not needing a god. An afterlife I don't believe in nor is there evidence for, so you cannot scare me with that.
3) The concept of heaven is ridiculous. In the approximately 80 years I have in my lifetime I will be judged on those actions and be put eternally in either heaven or hell? What if someone needed more time to 'repent'? What if someone wasn't given the chance to 'repent' because they died at a ridiculously young age? These people are supposed to suffer an eternity for their actions. Ridiculous. Furthermore, they don't even need to repent. They just need to believe that Jesus died for them. What about all the people who are never introduced to the person Jesus? They get put in hell because they never got the chance to even know who Jesus was. Any god or heaven which lasts an eternity which decrees such unjust requirements for acceptance I don't want any part of. Also, to take from a Talking Heads song: "Heaven is a place, where nothing ever happens." It's just good all the time with no challenges. That sounds really boring to me. But if heaven is defined as good, then it must fit whatever perfect lifestyle I want. That lifestyle is the one I live on this earth. So either heaven has to allow pain and suffering along with its goody bag or I should be allowed reincarnation. Buddhism sounds much more appealing. Lastly, to use a movie reference which probably references some philosopher, would humans even be able to comprehend their situation in heaven? A too perfect world and people might not even be able to cope with it and keep trying to wake up from. Maybe.
4) There's no certainty of which religion this god hails from, unless it told me specifically. But assuming it doesn't (something Christians cannot learn of either), why would I believe it was a god from Christianity, and not from any of the other major religions. They all have some things in common, such as spin-offs of the Ten Commandments. There's nothing much to be said here, because there is just that; nothing.
Conclusion: Even if there was a god, the god described by Christianity, I despise. I want nothing to do with that god, and will refuse to follow it, for I think it an irrational, vengeful, and unnecessary entity of whose rewards given are unwanted and prejudice.
