Imagine an orc-like species of violent sociopaths: they are sadists taking pleasure in the suffering of others, have fits of violent rage, see altruism and empathy as contemptible weakness and are all around complete jerks.
It is a truism that no-one consider themselves evil, but it is actually false: the Marquis de Sade (yes, the guy 'sadism' was named after) openly claimed to be evil, advocated for a form of ultimate freedom in the sense of "the freedom of wolves to prey on lambs" (with himself a wolf), and happily wrote (with the narrative flair of an IKEA manual) outrageously gore slash-fics to pass time when locked in by one government or another.
They would be kind of like that, but with the temperament of a hungover grizzly.
How could they form a stable enough community to be a problem to imprudent travellers or neighbouring settlements?
They don't need to be a major menace to the entire region, nor to be able to out-compete other societies on the long run, or even survive efficiently once the local Genghis Khan decides to do something for that envoy that came back in a few dozen packages. But they need to be a self-perpetuating society enough to survive generations, and ideally tend to make the rare non-chaotic-evil deviant either be driven back into the mould, flee or be culled.
Answers should if possible avoid advanced technology, magic, or improbable local conditions. The humanoids themselves don't need to be exactly humans - they can be stronger, heal faster and so-on, but shouldn't be too different from the variants of orcs that plague fantasy, so no demigods either. Or, if really impossible, explain exactly what makes it so unsustainable.
Ideally they should aim at being slavers, but also survive as a society when left alone, without external source of slaves.
Note: This question asks how a literally evil society works, but with the difference that it is the society itself that is evil, not the individuals that are all ill-tempered sociopaths. Several answers describe organised societies striving to an evil goal, but this requires individuals to be rational and have self-control enough to work together toward a common goal on the long term.