Yankovic came up with the idea for Fat while watching the Bad music video, when he had an epiphany that a parody of that song titled Fat would be a good sequel to Eat It (a previous Weird Al Michael Jackson parody). As he watched the Bad video, he imagined an obese version of himself trying to get through the turnstiles on a subway, and resolved that he would do it.
When performing in concert, Yankovic wears a fat suit and a mask that makes his face appear fat. Due to undergoing laser vision correction surgery, he no longer needs to wear glasses, though he wears glasses with non-prescription plastic lenses in order to help hold on the mask.
The video for "Fat" parodies various elements of the "Bad" video by Jackson; Yankovic was able to get permission from Michael Jackson to use the same subway set from "Bad" for the video. Here is a list depicting some parody elements:
The lighting in Jackson's video is much darker. Yankovic filmed his parody video with much brighter lighting, and it appears as though it was filmed in the daytime.
The video begins with a non-musical black-and-white scene, as in the original, but it is much shorter. It starts at the subway station with a gang of obese men (led by Lou B. Washington, who soon after joined the cast of Al's film UHF) criticizing Al for not eating much unhealthy food lately. They try to get Al to eat a slice of pizza, a hamburger and a Ding Dong, which they pull out of their pockets. The original video showed Jackson coming back from high school and his old street friends bugging him about going to school and becoming soft.
The lines "Are you fat, or what?" and "You ain't fat, you ain't nothing!" mimic lines in the original, only using the word "fat" instead of "bad".
In the beginning the dancers can be seen goofing off. Two of them miss a high five, while another can be seen waving and mouthing the words "Hi Mom" over and over again, and is pulled away from the camera by another of the dancers by his nose. As a whole the group looks disorganized and fidgety, as a parody of the precise choreography in Michael Jackson's video.
Yankovic has six dancers. The original video has Jackson with at least twenty dancers.
The six dancers with Yankovic in the video are obese instead of skinny. They are also dressed similarly to the dancers in "Bad." In order to get the dancers Yankovic simply advertised for "very fat dancers" in a trade journal, and his hunch that such people might exist was soon proven right. Yankovic stated in the liner notes for Permanent Record: Al in the Box that one of the dancers was actually a pizza delivery man who delivered pizzas to the casting office (he was put in the video because he had the "perfect physique", according to Yankovic).
Instead of a troupe of dancers sliding along the ground, the beginning of "Fat" shows Yankovic getting fatter and fatter.
Yankovic's black outfit is similar to Jackson's, but the buckle and zipper ornamentation is exaggerated.
Yankovic does Jackson's famous "crotch-grab", but with humorous sound effects added, such as a "boing" and a cowbell.
When Yankovic tries to jump over the turnstiles on the first bridge of the song, he can't get over. Jackson, by contrast, easily jumps on then off.
In one musical interlude, Yankovic jumps on a dancer and crushes him while Jackson merely jumps on his shoulder.
In the middle-end, the dancers and Yankovic moving in a line close together trying to go fast and slightly succeeding in doing so, while in "Bad", the dancers are doing the same thing but slower and easier.
In "Bad", Jackson moves in a circle while the camera follows him. In "Fat", Yankovic does the same thing, but for much longer. Eventually, Yankovic moves too fast, and begins to fly. He grabs a hold of the tripod to not fly away, but loses his grip and flies off with a startled cry.
When Yankovic flings his arms around, sound effects are heard. This is direct reference to the noises heard when Jackson flings his arms. Yankovic acts confused testing out the sound effect movements, and moves other parts of his body, making other sound effects. Al's dancers also appear confused.
In "Bad", Jackson and his dancers scream loudly for no reason at random times. Yankovic parodies this by having a scene where he and his dancers scream "Ho!" every now and then. One of the dancers hands Yankovic a gardening hoe, and Yankovic comments on it by saying "Hoe!" This also occurs when the song is performed live, though, occasionally, a man in a Santa Claus suit comes on stage and is belly-bumped (or, as seen on "Weird Al" Yankovic Live!, punched in the face) by Al. In the Straight Outta Lynwood tour, in keeping with the "gangsta" theme of the latest album, the man dressed as Santa was replaced by a man dressed as a promiscuous woman. Al points at the visitor and shouts "Ho!"
The camera follows Yankovic and the other dancers as they run through the station, when Yankovic is handed the gardening tool. After a brief pause, he and the others realize the camera is still moving, and they start to run again, moving even faster to try to get into the camera's viewpoint (now yelling "Ho!" to get the camera to slow down). Eventually they disappear off-camera. Upon returning to where they left off it's discovered that they are now catching their breath from the running that Jackson and his troupe are able to do easily. Yankovic leans against a pillar and tilts it.
When Yankovic runs up the steps and removes the air vent cover, he spins and flourishes excessively in a parody of Jackson's dancing advance towards the vent. Also, the wind in this video is much stronger. Several dancers get blown away, and Yankovic holds up a pinwheel, and stays standing as his dancers are blown out of sight. A chicken is seen passing by the camera.
Instead of dancers dancing near the end, the dancers can be seen bumping into each other. In this scene, the word "FAT" is spray painted on the wall instead of "BAD".
At one point near the end, Jackson whoops three times in a row. The third time, Yankovic holds up a speech bubble containing the word, "Woo!" instead of actually singing it, satirizing the voice synchronization of Michael Jackson's video, in which several scenes are seen with Jackson mouthing words that are not heard.
The wanted poster near the end is different. Instead of, "Wanted for sacrilege", with the word "BAD" below, it states, "Wanted for gluttony", with the word "FAT" underneath.
The man in the roller skates walks very slowly and with much difficulty, while in "Bad", one of the dancers is seen doing a version of the moon walk where he is not moving at all.
When Jackson and his group run up the stairs nearing the end one of the dancers does a continuous amount of backflips, in "Fat" one of Al's dancers tries to do a single cartwheel and barely makes it. (Although he celebrates as though this is a great success.)
In "Bad", Jackson screams at the end of the video. In "Fat", Yankovic screams for a reason: his fingers are caught in a mousetrap that seemingly came out of nowhere. The same sound effect is used for the trap as from earlier, when Yankovic was waving his arms around.
Finally, at the very end, Yankovic says "Who's fat?", while Jackson says "Who's bad?" The video stops with a close up shot of Yankovic holding his fist. In "Bad", it stops with Jackson a foot away from the screen, although on the full version of the video, he sings a bit longer, as the parts are in the original song, while the parts are not in "Fat".