The Blob, member of the Brotherhood of Evil Mutants. His weight and physical appearance are played up for horror and squick whenever he shows interest in a woman. In a bit of a subversion, his weight comes not from overeating but his mutation. When he was depowered, he ended up as his true weight - which was incredibly thin. After plastic surgery to remove his excess skin, he ended up being a pastiche of Jared from the Subway commercials. In the animated series and Depending on the Writer, he's still a greedy, slovenly, unhygienic pig, though. The animated series also tends to imply he is fat because of his eating habits.
Dialled Up to 11 with the Ultimate Universe version of the Blob, to the point where he once paused during an attack on the Avengers Ultimates' mansion to raid the fridge. Less funny was the time he was discovered eating the Wasp's corpse.
The Age of Apocalypse version was just as bad, if not worse - there was no indication that Ultimate Blob necessarily killed the Wasp, simply being an Opportunistic Bastard in the most horrifying way possible. Ao A Blob, by contrast, killed and ate Ao A Nightcrawler's wife (possibly alive), then later taunted him about it. Nightcrawler, not having his canon counterpart's scruples, responded by teleporting a shark into his stomach and letting it eat him alive. Yeah, the Age of Apocalypse is a horrifying place all round.
Also from X-Men is the alien Mojo, a sort of fat evil television executive.
When Shadow King possessed Karma for several months in New Mutants, she became ludicrously bloated through Farouk's gluttony. She got better, thanks to the Desert Starvation Diet.
Another example from Spider-Man's corner of the MU would be Nick Katzenberg, a Daily Bugle photographer, paparazzi, and rival to Peter Parker. While not a villain, Katzenberg was sleazy, immoral, and generally unpleasant, as well as a Fat Slob.
Also in the Marvel Universe is the Slug; a drug czar who makes the Kingpin look svelte. He is so obese he cannot move without the aide of a motorized wheelchair and can suffocate people in the folds of his flesh. One source says he weighs 1,200 pounds. (Creator Mark Gruenwald remarked when the character debuted, "At the time, I thought a 1,200 pound man was a bit far-fetched, but I've since read about such a guy in People.")
This Trope is massively subverted by Big Bertha, a supermodel who has several 'brick' superpowers, including invulnerability and superstrength, and the ability to change shape but only into an obese (if she were not superstrong, she would likely be immobile) version of herself. Since no one recognizes the obese form as the same as her normal form, and in fact she only has the brick powers whilst in her fat form, she only fights crime as an obese person.
One Hulk story had a one-shot villain by the name of St John Hubert who captured the Hulk to replicate his powers. He was morbidly obese and could only walk with the assistance of crutches and although he succeeded in inducing a gamma mutation, it just made him an even fatter blob.
The cynical fatty tabby, Garfield. Other than abusing Odie and making his owner's life hell, he does nothing but eat and sleep.
Both Roark brothers in the comic version of Sin City are overweight and look unhygenic. Herr Wallenquist also has this look. They are all extremely evil crimebosses.
A lesser example would be Agamemnon, the sleazy porn-obsessed boss of Dwight and later, Wallace. He was an art dealer that was overweight, ugly, and smelled bad. He didn't pay well, either.
Subverted with Sam from Spawn. While he caters to every single characteristic of the trope, he's as good a guy as they come who always strives to right wrongs. The bastard tendencies tend to be directed towards bad guys. Clown (aka Violator), Tony Twist and Billy Kincaid, on the other hand, play this tropestraight.