This is typically called black humor (based on an essay by Andre Breton). Personally, I dislike the term, because it sounds racial when it isn't, but it is commonly used and well-understood ("bleak" humor is a soundalike alternative). It isn't always about cruelty, but it deals with grotesque, obscene, taboo or otherwise usually unfunny subjects. The most well-known subgenre of this type of humor is "gallows humor," which is specifically about death.
Physical comedy involving pain, cruelty and violence, but as played for lighthearted uncomplicated laughs, is called slapstick. In contrast to black humor, however, slapstick is usually cartoonishly unreal, and completely consequence free.
If you combine the two, you end up with what is variously called a bleak, black, or tragic farce. Death at at Funeral, The Ladykillers, Heathers, Accidental Death of an Anarchist, Movie 43, and Tropic Thunder are a few examples that come readily to mind, or, for something more reminiscent of Tarantino, Once Upon a Time in Mexico.