"Fat" is a song by "Weird Al" Yankovic. It is a parody of "Bad" by Michael Jackson. It is the second parody Yankovic did of a Jackson song, the first being "Eat It", a parody of Jackson's "Beat It". "Fat" is the first song on Yankovic's Even Worse album.
Nowadays, when the song is performed in concert, Yankovic wears a fat suit and a mask that makes his face appear fat. He also wears glasses for this song, which were needed to hold the mask on.