The Mandingo fights. Also the slave who was torn apart by dogs.
The cold demeanor of the "winning" Mandingo being congratulated by Calvin Candie. He is either a remorseless killer, or he's been desensitized to the horrific situation he is in in life.
Also, Candie treats him like he's just done some hard work around the house, and not break a man's arm, gouge out his eyes, and then kill him with a fucking hammer to the face.
Just about any of the scenes showing the brutality of slavery. Tarantino pulls no punches.
Some people just won't die. And they keep getting shot.
Calvin Candie is really, really creepy and deranged when he is pissed.
The scene where Billy is willing to castrate Django.
Stephen is blood-freezingly calm as he tells Django about how he will send him to the mines, how any atrocity they may inflict to him pales in comparison to that, how for Candie's death he is gonna suffer to the last breath.
The first shootout in Candieland, after Candie's death. Even for an awesome moment, it is quite disturbing the fact that is possibly one of the most bloody and brutal shootings in film history, on par with the Grand Theft Auto V stuff.