A lot of the imagery surrounding Scar is intended to communicate his utter vileness. There's the scar on his face, for one. And then there's all the green smog and oozing lava that show up whenever he's partying in the elephant graveyard.
But there's one Scar scene that's downright iconic. When he's first rallying the hyenas to kill Mufasa and Simba, he sings a song called "Be Prepared." The hyenas get pretty jazzed by the song, and they form an ad hoc army, marching past Scar while he sings from atop a giant outcropping of rock. Here's a little memory refresher.
That image isn't exactly unique. It's drawn to resemble the Nazi rallies of the late 1930s. The hyenas are goose-stepping Nazis. And Scar is supposed to be Hitler. Yep, you read that right. Here's a photo of the real Hitler for comparison.
It doesn't get much more evil than a Nazi rally, Disney. You got your message across.