It depends too much on way too many factors. Generally I’ll be almost as polite as they’re being.

Convos usually involve turn-taking though, so once you’ve provided evidence or a sound argument, you should not be forced to do it again. It should be their turn to assert something, and then possibly have to provide whatever.

Just don’t let the opportunity pass to treat them exactly, or potentially slightly worse, depending, than they’re treating you. Don’t stay on defense, assert, ask questions, directly contradict, whatever is needful.