The second line of discussion in this series. Besides "dark fics", another classification that doesn't seem to have a universally agreed-upon definition (but that my one-shots often get called) is a "crack fic".
The general gist is "a fic that makes you go WTF" or "a fic that makes you think the writer was on crack". But because this category is less looked for than its cousin, the "dark fic", there isn't as much controversy over its actual meaning. For example, slash fics make me go WTF personally, but they're not generally considered crack fics. I personally consider comedy one of the elements of a crack fic, but many people think it is not so.
What makes a fic a "crack fic" in your opinion?