Yeah. I know 100% what you mean. It is hard to maintain good humor. If it helps:

1. It's fun to deal with the ones that are doing a really shitty job. I was happy seeing this guy come in and instantly trip over his dick trying to say "all NATO's fault" in this obvious and incompetent manner. I don't think it actually needed debunking really, but maybe a larger number of people laughing at him in the comments will result in a bad performance review or something along those lines.
2. Don't feel like you need to deal point-by-point with their horseshit. You don't need to be evasive or deceptive or anything, but they don't deserve the courtesy of a detailed and factual counterargument. If you answer one argument, they'll just pretend you didn't and raise another. You'll notice that except for the end, I basically ignored almost everything he said, because it's not like it really needs debunking. I just took the chance to talk about some stuff that counterbalanced their narrative and I felt like talking about.
3. Don't feel like you need to be polite. I've actually seen some writings that dealing straightforward-factually with this kind of stuff actually is just not effective and more or less gives them a platform, and I can completely believe it. Don't be unhinged or hostile, but also, don't pretend you respect them. The social contract goes both ways, and honoring it with someone who's breaking it is just being a chump and sending the wrong message to people reading.
4. If they do decide they want to debate, I love to just ask straight questions. I recently got banned again from Hexbear because of some participation that included:

• Hey, quick question: Why did Russia swear before the invasion that they were not going to invade Ukraine, and any reports of that were just Western lies?
• Why did they change the goal from “denazification and demilitarization” to “we need to keep all this extra land on the border because it’s ours now and we’ll keep killing people until someone gives up and lets us have it”?
• Is Russia’s current set of actions more likely to produce the result: More motivation to join NATO by neighboring countries, or less motivation?

There were a couple of other ones, sort of detail questions related to what we were talking about. They really get irritable when you just ask straight questions that their framework doesn't like the answers to. Zero of my questions got answered even when I pointed out that maybe they had overlooked the question or meant to respond to someone else and politely asked it again, and they accused me of "JAQing off" and said it was a horrible thing to do to ask them these things. (Killing people apparently is okay.)

Be sarcastic. Be insulting. After all, they are wrong, and they're killing people. I'm not trying to be embittered about it or anything (and sometimes I am not successful in that) but it's okay not to be nice to them.