Fancid

Fanwork + Rancid = Fancid

Describes a piece of fan-made work (usually fanfiction or fanart) that turns the original TV / Movie / Book series into something shitty (or shittier, depending on the series).

A fucked-up rendition of the original series, but is usually seen as a success in the creator's eyes.

Usually, but not always, includes (a) Mary-sue(s) and / or (a) crack pairing(s).

Fanart and fanfiction created for humor purposes is usually fancid, but that's what makes them funny in the first place.