The threesome scene
(Movie and Book spoilers ahead)
In the book, Alex goes to the music store where he lures two 10 year-olds to him bedroom, and them abuses them. Disgusting.
In the movie, he seduces two young ladies and has consensual sex with them. Everybody seemed to have fun, he was not even rough. Kudos to him.
I understand pedophilia might be too heavy for the screen, but what was the point of showing that scene, then? It looked out of character and gratuitous.