I've heard this one a few times. "Atheists don't have to prove anything because atheism is the null hypothesis. You disbelieve something until it is proven."
This is the kind of thing I want to record and play back to people so they can see how dumb they sound.
Let's all go back in time four hundred years.
I'll go up to a local and say "Hey, in a few hundred years we will all have glowing boxes that we put onto desks and send each other pictures of cats doing silly things to people all around the world."
If the person says "Sounds great." then that's fine, though you have to wonder if you can test their gullibility somehow.
If the person says "Prove it.", then I've got some work to do, and that's absolutely reasonable.
If they person says "I don't believe you." they would be absolutely wrong and they'd have to explain their reasons to me.
The best, most honest, and truly neutral position to take about the unknown is simply saying "I don't know, but I'm open to it."
If you start saying the person making a claim is wrong, then you need to have a reason to think so.
When it comes to belief in God, the "I don't know, but I'm open to it." position is agnosticism, not atheism.
This 'null hypothesis' stuff about believing the negative until the positive is proven is absolute nonsense. When there are only two options for truth, you don't believe one just because there's no evidence for the other (especially if there's no evidence for either!).
