The movie is essentially a cruel revenge tale, with bad behavior met by more bad behavior.
The character is abducted and imprisoned for 20 years. He bashes his head against the wall and tries to kill himself. Upon his release he beats up dozens of men, including some innocent bystanders. He bashes people in the head with a hammer, and gets a knife stuck in his back. Characters are tied down and tortured. In a flashback, a father kills his entire family, and himself, with a shotgun. Lots of blood is shown. We also see a bloody suicide. There's an attempted rape.
There's a graphic sex scene with female toplessness and male and female backsides shown. The scene takes on a greater, and more disturbing resonance after the big reveal at the end. Another sex scene is in the dark, but you can hear sounds. The character is shown masturbating under a pillow while watching a workout show on TV. Incest is part of the plot. In an early scene, the character attempts and fails to seduce a woman during a business meeting.
Language includes several uses of "f--k," "s--t," "bulls--t," "bitch," "dick," and "piss," plus "Jesus H. Christ" and "Goddamn."
Apple iPhones are shown. Google searches are important to the plot.
Drinking, Drugs & Smoking
The main character starts the movie as a hardcore alcoholic, pouring vodka in a paper cup to make it look like he's drinking soda. He's shown raging drunk one night, screaming on the streets and searching for more booze. (He's also shown smoking a cigarette.) During his imprisonment, he's given a bottle of vodka a day, which he guzzles down greedily. Eventually he stops drinking through hard work and persistence. An old friend of his is also a strong drinker, seen with a glass of whisky at all times. Another character is said to be a former drug user, but recovered.