Crack Pairing

"Crack Pairing" is a term used to describe a pairing that lacks canonical basis or supporting evidence, and therefore seems unlikely to occur canonically. They are typically formed from characters that exhibit a lack of communication or interaction in the show, or any other form of authentication. The name stems from the notion that the author must have been ingesting some illegal substance just to think up the pairing, let alone write it. Their origins are often popular fan works or character similarities.
Though the term can apply to some popular ships, it is most often applied to pairings that are meant to be humorous in their randomness. These are created by pairing up two random characters with no previous interaction or chemistry, and is often considered the result of a challenge, either from someone outside the author or from the author him/herself: "This pairing is completely unworkable, but I bet I can make it work."
This definition is not exclusive, however, as Crack Pairings can also arise from character similarities, such as two characters sharing an interest, off-screen interaction or from popular fan works that seek to form the basis of future fan works, rather than canonical evidence.
The term is similar to Rarepair - however, a 'crack pairing' has a lack of evidence but can be popular while a 'rarepair' is defined by popularity.