The onus is on those who claim the existence to do so,you cannot shift the burden of proof to someone else. This is what Russell's teapot was meant to illustrate. Nobody has to prove anyone's fantasy false,it is up to the person making the claim to prove it. I have had theists saying they didn't think I had any right to demand proof and they could believe what they want. Not if you are dissing scientific theory you can't. If you want to assume a God exists without proof,you have no right to diss someone else's views that has proof,either shut up or provide evidence. Another tact,is agreeing to differ,or saying 'that's just your opinion' which is a means of shutting down the argument as if both opinions carry the same weight,they don't. One has evidence and the other does not. Either be intellectually honest and provide evidence and proof or don't enter the argument. I don't have to prove your unsubstantiated opinions faulty.