Today's contender is a corker from Stephen Roberts that fundie atheists love to quote. It's the type of catchphrase that gets them out of actually having to think about anything. Their favourite kind! Along with 'atheism is the null hypothesis', and 'atheism and agnosticism are essentially the same thing'.
Anyway, let's look at this one:
"I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours." Stephen F. Roberts
The first bit: "we are both atheists". Simply put - no. Even granting the dumb 'lack of belief' definition of atheism that many fundies cling to, atheism is a non-belief in any gods. It's the belief that the world and universe exists and functions without a god involved. You're not an atheist one hundred times over for not believing in one hundred gods. You're an atheist if you rule them all out without exception.
A theist is someone who believes in at least one. You can't be a theist and an atheist. They're mutually exclusive positions.
But, yes, you can believe in one, and none of the others. Even though the phrasing is ridiculous, I guess that's the point that he was attempting to make.
The second bit: "I believe in one fewer god than you do". This betrays a bias that's common among fundie atheists. They really dislike the God of Abraham. The one that Jews, Christians, Muslims, Mormons, Baha'i, and Rastafarians believe in. The 'one god less' phrase doesn't work if the quote is said to a Hindu, or someone who still believes in the Greek pantheon. Hindus have millions of gods. Does the number change anything? Does their having several million mean they are more likely to be correct? Somehow the phrase "We're both atheists, I just believe in three million less gods than you" doesn't have the same ring to it.
The last bit: "When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours". This is clearly making assumptions about what I think about the other gods. It's assuming I dismiss them. It's assuming I dismiss them for the same reason he dismisses mine. It's assuming the other gods are similar to my god in every way. There's no basis for any of those assumptions.
Firstly, I don't entirely dismiss the other gods. I do put them in a different class, probably not worthy of the title 'god'. I think it's entirely plausible that in keeping with Christian theology that the gods of Ancient Greece, Rome, Egypt, and Norway etc. were fallen angels or Nephilim. That's comfortable.
I haven't personally studied the evidence and arguments for and against the definitive existence of any of those 'gods', and although I treat their stories as no more than myth, I haven't got solid reason to completely dismiss them. So I don't.
What I think Stephen Roberts' and his fans train of thought is "I think Greek stories of gods are myths, therefore the gods never existed. I also think the Bible stories are myths, therefore God never existed."
But that doesn't even work anyway. As I said, the Greek gods and the Christian God are a different class of being. The Greek gods are always something like Zeus, son of Cronos. They are created beings, they live on the planet and have physical bodies. They are very powerful, but they have more in common with Superman and the Flash than Yahweh. Yahweh, the God of Abraham, is a purely spirit being, who is the uncaused cause of the universe. He's the prime mover - nothing would exist without him.
That's the first difference. The second difference is that the Bible is rooted in history. Archaeology and ancient literature support much of the Old Testament and all of the New. Greek mythology seems to always have been open for poets and playwrights to do as they liked with. No one makes any assumption that Homer thought he was presenting a true story when he wrote 'The Odyssey'. To this day scientists, historians, and philosophers are finding more and more evidence for the prime mover and being able to match what they find to what the Bible describes. 'The Twelve Labours of Heracles' doesn't compare.
So even if it can be shown that every story of the Greek gods were myths written by poets, it doesn't carry over to the Bible, which was written by preachers, historians, and kings.
So the assumptions are completely off base. I don't completely dismiss the other gods. My reasons for thinking that they are not the true gods are based on strong evidence and historical study. My reasons for kind of dismissing them are not the same as his reasons for dismissing mine.