It’s difficult to point out what the absolute worst argument is from believers. They are so many choices. But at least one of the worst has got to be when they attempt to dispute that the burden of proof lies with them, not atheists or agnostics or anyone else not making the positive claim. Granted, most theists just ignore this argument rather than engage it, but every so often I see someone attempt to refute it.
And then I chuckle. With a grain of sadness.