Remember the original discussion and don't take the bait to deviate. "We are not talking about X, we are talking about Y as originally posted by OP and I will not follow you down your rabbit hole."

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.

i don't answer questions (present thread excepted). i insist someone say plainly what it is they are getting at. and if they refuse that's that. if they persist in asking, i tell them not to be petulant. and if they present an argument, and it's sound, i usually just let that stand. if it's unsound, i let them know.

and, of course, one of the best ways is to never take a strong position yourself that can be sealioned.

For me, relentless mockery is best

Inform them that you're wise to their game, and furthermore, they're an idiot. Doesn't cede the field to them but doesn't let them persist in bad faith questions.

Internet arguments are like a rock paper scissors game of evidence based arguments, sealioning, and good old fashioned trolling.