This policy applies to any mainspace article. Uncategorized articles look bad, just don't put them in. Most humor falls under a few specific categories (i.e. language, food, animals, medical, religious, and technical), but if there is no category that works, create one. However, redlink categories look bad. Really bad. So make sure to add something that describes the category.
If an uncategorized article is created by a user, one of our admins will fix it and drop a friendly reminder on the user's talkpage. If this happens a second time, another, more serious, warning will be issued. Do it a third time and that will result in a one-day block.
Remember, this is a humor wiki, and, as with humor, we are not going to be troubled if you forget to categorize your articles. Everyone's stay here should be enjoyable, and this policy is just a safeguard. However, it doesn't mean you should not categorize your articles.