I've noticed, and posted before on this, both here and on FB, that the consignment to hell means that the theist party has run out of argument.

Well, first, that point is moot because atheists don't believe in the existence of Hell and, second, you can ask them if a religion based on fear is worth following, even if it was right. I'd say "screw you" to any deity which would punish people just for not believing in it, even if it lead me to eternal damnation; such a deity would not deserve our worship, even if it existed.

Not all religions believe in a heaven or hell. You could point that out to them and ask why they think their religion is the one true one.
You could ask them to give you a detailed definition of their god.
You could ask them to show you testable, falsifiable evidence for the existence of this god.
When they can't do any of this (and they won't) you can easily tell them that the conversation is no longer worth having.

That threat is only about fear mongering. It is a cowards way to deal with life. So ask these people if they think cowardliness is a prerogative for heaven? .
I think the Willy Wonka Chocolate Factory story is a good example.