I'd recommend blocking the entire channel each time you see a video like this, and also go through the top hundred recommended videos or so and block all the channels with content you don't like. I've only blocked a few dozen channels, and we barely see any of this stuff now. The UI might be a bit confusing, because you can only block a channel if you're currently viewing a video from it.

I do wish I could just whitelist channels, or get automatic recommendations for channels to block.