She's like Mussolini and your nosy old neighbor, all rolled into one.
The short-lived headmistress of Hogwarts gets off on torturing children, has an unflinching holier-than-thou attitude and, unless David Yates has something stashed for an extended edition of the films, *SPOILER* she gets away with it. *END SPOILER*
Well, unless you count the part where she is abducted and gang raped by centaurs in Harry Potter and the Order of the Phoenix. And if you think we're just filling in the rape stuff with our filthy imaginations, hang on.
Near the climax of the book/film, Umbridge is hauled screaming into the Forbidden Forest by a group of centaurs. No one sees what happens next.
What you have to realize is that there's a reason Rowling made sure it was centaurs who snatched Umbridge, rather than any of the countless other dangerous creatures in the forest (like the giant spiders). If you're familiar with the mythology of centaurs, seeing a screaming woman get hauled away by a bunch of them gives you the same feeling you get in Deliverance when Ned Beatty falls into the hands of the hillbillies, or when Bruce Willis and Ving Rhames wind up imprisoned by the same in Pulp Fiction. Centaurs rape human women -- that's what they do, that's a central part of their mythology.
In one legend, centaurs were invited to a wedding feast and attempted to rape the bride. In another, the famous centaur Nessus was killed while trying to rape a woman. That's the point of centaurs as characters -- they have the heads of men and the animal urges of horses.