The act of taking a single (often minor) aspect of a character and exaggerating it more and more until it's huge and cartoonish and almost entirely consumes the character. Sitcom characters are particularly susceptible to this, as are peripheral characters in shows with long runs.
This can become very annoying if the character's aspects were originally unique and subtle, only to become more stereotypical as the story progresses, to fit the requirements of more cliche plots. Especially dangerous if executives think doing this will appeal with their demographic better and boost ratings.
Named for one of the many unfortunate victim characters in The Simpsons, Ned Flanders, who was originally just a clean-living, somewhat religious fellow.
Makoto in School Days transforms from a merely sex-curious teenager into an uncaring, womanizing bastard. Furthermore, the two main female love interests get reduced to their obsession for Makoto only.