And then I had an idea — what if you were only allowed to say sentences that had never been said before, ever? A bot with access to the full channel logs could kick you out when you repeated something that had already been said. There would be no “all your base are belong to us”, no “lol”, no “asl”, no “there are no girls on the internet”. No “I know rite”, no “hi everyone”, no “morning sucks.” Just thoughtful, full sentences.
Notes: This is for chat. It would probably be a bad thing to eliminate cut-and-pasting what you're replaying to, as is usual in slower sorts of conversation.
This is intended to improve conversation among people of good will. You still need human moderation to deal with griefers, spammers, and other such parasites.