For adult themes. There’s no sex in No Exit, though Garcin and Estelle dance around the topic for much of the play. There are certainly plenty of stories about sex and relationships from the characters’ lives back on earth: Inez is a predator who broke up a marriage and indirectly caused a man’s death. Estelle cheated on her much older husband with a younger man, and drowned the resulting baby. And Garcin cheated on his wife.
Come to think of it, all the sex in No Exit is negative, destructive, or even deadly. This might have something to do with Sartre’s perspective in Being and Nothingness that sex is an attempt to objectify, which always backfires and ends up objectifying the self. (See Estelle’s "Character Analysis" for a full discussion.)