Beat them at their own game with some new lesser known fallacies.
OR
Just keep asking, how do you know that?

Beign aware of logical fallacies can keep you from being conned or duped.

There's a group here called street epistemology or something like that that has some interesting stuff on deconversion, including some how to stuff on dealing with exactly that issue.

Your question sets us (the question takers) up with a false-dichotomy fallacy; there are many ways to approach this question, such as gently approaching the fallacy user (in some cases, particularly if you know them on a personal level) and explaining why their assertion of 2 + 2 = ∞ – 1 (or something, occasionally, less absurd) doesn't add up. That third option (and a range of responses around it) is where productive dialogue can take place.

it depends on what kind of stake i have in busting those fallacies. i choose my battles -- wisely, i hope! so sometimes i just dismiss them. other times i may take the time to point out the fallacies one by one.

g

I try to use logic to help the see my point of view. If it's a constant problem, I lessen or eliminate my interactions with them.

depends how drunk i am

My advice would be to just ignore them, but who am I kidding here. Most of the time I can't just ignore that bs.