It says so right on the box the deck of cards comes in. “Cards Against Humanity: A party game for horrible people.”
The easiest way to explain Cards Against Humanity’s premise to newbies is “no-limits” Apples to Apples. It’s for people who have always been frustrated that Apples to Apples deliberately left out questions like “How did I lose my virginity?” and the incendiary possibilities of answering them with cards like “Eugenics,” “AIDS,” and “Binging and purging.” People who are constantly suppressing the urge to make the most obscene, offensive jokes that spring to mind. People for whom a game that openly invites such jokes is a liberating catharsis.
You know, horrible people. People like me.