It's your free will to slap me, it may be that out of your free will decision there comes an opportunity for me to show you how and why I believe in God, but I don't know what His plan is... just of note, I wouldn't suggest slapping Christians as part of an experiment to see whether this relates to His plan... it may after all be that His plan is for you to turn to Him after being jailed for assaults on religious groups ;)
Honestly, I can't tell you what my criteria would be. That's not because 'nothing will prove it', but simply because of my own human weaknesses. I honestly could not tell you what would 'prove' God or any other deity exists because it could be a trick akin to the bunny-from-a-hat. It could be some new science. Sleight-of-hand or even a hallucination. Unfortunately the Veil of Perception prevents me from being able to say with 100% certainty what it would take for me to believe God exists. However - I will still give anybody who wishes it the chance to submit evidence and I will evaluate it. It would definitely have to be something repeatable and subject to physical scrutiny by others.
I just don't like wilful ignorance.
Hitchhiker's, just because.
'I refuse to prove that I exist,' says God, `for proof denies faith, and without faith I am nothing.'
`But,' says Man, `The Babel fish is a dead giveaway, isn't it? It could not have evolved by chance. It proves you exist, and so therefore, by your own arguments, you don't. QED.'
`Oh dear,' says God, `I hadn't thought of that,' and promptly disappears in a puff of logic.
Original sin and pennance [or at least how pennance is presented] are both the belief that you are sinful because you exist [or because of someone else's actions]. You may not have actually done anything, you could be the most pious person in existence. But, you're still sinful and should beg for forgiveness.
[Hey, look Godwin!] Think of it like judging everyone based on Hitler.
If someone claimed to be Jesus, would Christians HAVE to believe them? According to their religion Jesus was real, was the son of God and will come back to kick of the Apocalypse. [I think...] So, it logically follows that said person COULD be Jesus.
Personally speaking, if you're searching yourself for any sign of existence of $deity, then that's normally when you will find the proof you need..
The thing (and this can be applied to anything really I guess) - if you're looking for something, you're more likely to stumble upon the proof that you require, where as if you're not searching, then you're not likely to accept any proof..
For me, I've always known about God, I was brought up knowing of God, I went to church with my Christian Mother and Atheist Church Organ Playing Father, I lost "faith" in my own faith for a while, but it wasn't until I had a few God encounters at various places along my journey that He became real for me. And those things keep happening for me. Everyone's journey is different, some don't find that proof, some are happy not even looking for that proof.
However, my pet hate in any of this is when people try to bully you into thinking their way about things, or try to belittle other people's beliefs / non-beliefs (whatever the PC all encompassing term is). If you want to believe in a God, any God, great, that's brilliant, I'm truly happy for you, if you want to have a shared journey whilst believing in the same God as I, that's great too, if you want to not believe in anything, that's totally fine, the one thing that you must do in all of this though is be respectful to those other people around you. Not to take pot shots at people because of their differences of thought, but to have grown up conversations about it. Not to get angry saying its up to you to prove this that and the other, it's not up to anyone to prove anything to anyone in this sense, your life is your life. Its up to you as a person to explore different things and not just take something as being said as being the truth, it's up to you to have the discussion, in a grown up way, with people of differing views, and only from that will there be a chance to prove it.
For me, God didn't command "go out and prove I exist" he said "go and make disciples of men" - this is about leadership, not conning people into stuff, not promising peoples answers you can't give, but living your life as best you can, and people will be attracted to the things you do.. now this might be that you go out and your just a really nice person who doesn't have a belief, but people might put faith in your non belief and go along with that, or they might just be happy to be, equally, people might (as I've had people with me) come up and say things such as "are you a Christian" to which when I've confirmed this they've simply said "I thought you might have been, there's just something different about how you are with the pupils and staff, a kindness that just seems to shine out" - now I'm not saying that non-Christian's can't have this, they can have kindness, and do have, towards people - but if you're going around with a chip on your shoulder about religion and spouting off to try and belittle other people, then, well, you're just not a nice person in the first place.
We're all in this world together, and (at the risk of sounding like a complete hippy) we are all different and just need to accept that and be at peace with that. They say the biggest cause of grief in the world stems from religion, no, it stems from the misinterpretation of religion. I'm not sure there is a single religion out there that states "in order to make these people believe, you must kill yourself and take out as many people as you can whilst doing it" - this is where religion is used as a tool to guilt people, and it comes back to the same thing, it's not the way we should live, with or without religion.
I'm really glad that this discussion has actually been undertaken fairly well actually, apart from the odd thing. People are allowed to get passionate about their own view points and put them across passionately, but if it can't be done with respect, then just shut up, I don't want to hear it. :) [/rant2]