I was using "blacklist" in a much more general sense, but here's how it actually plays out. Most of my general purpose website reading is done through an RSS aggregator. If one of those feeds starts using genAI, then I just drop it out of the aggregator. If it's a website that I found through web search, then I use Kagi's search refinement settings to ensure that site won't come up again in my search results. If it's a YouTube channel I subscribe to, I unsubscribe. If it's one that YouTube recommended to me, I tell YouTube to no longer recommend anything from that channel.

Otherwise, I just remember that particular source as being untrustworthy.