Just in case anyone missed it in the opening paragraphs, Fat Bastard from the Austin Powers films is the Trope Namer. He is an ill-tempered Scot who weighs a metric ton and Eats Babies.
Though the end of his debut movie does try to paint him in a sympathetic light for about a minute or two...and then he blows it by farting at the end of his heartfelt monologue, and decides to kill Austin and his Love Interest anyway.
Zigzagged with Jelly, Paul Vitti's right-hand man in Analyze This. He is fat (likely how he got his name), he is a mobster (and he has killed a few people in his career), but he's more of a Noble Demon.
Cross-dressing John Waters star Divine, playing a man, was always unsympathetic and unlikeable. As a woman, at least "she" was the protagonist (extended to non-Waters movies like Trouble in Mind and Rustlers Rhapsody.)