Humor is not banned and nor should it be. But maybe, to avoid confusion we could make humourus posts have a * or someting? And maybe humor can live in a separate section of the site so it doesn't mix with the other content. But if it still doesn't work I think we all know of a final solution for humor.
Maybe we could have a different upvote system, like marking a post +1 Funny vs +1 Insightful. Then users could adjust their own personal scoring if they don't want to see humorous posts.
