First up, I'd sit him down and explain that you will take him at his word. That means that if he says he's ok with something he's not actually ok with, then he doesn't get to blame you when you do what he said you could do.
Then do it. Take him at his word.
He says he doesn't want the last cupcake? You eat it. He doesn't care what you watch on TV? You choose and he doesn't get to complain. He says to do what you want with a new friend? Do it. He asks for the juicy details? Show him the video (ok, that's probably going too far, but you get the point). Eventually he'll get used to expressing himself honestly because he'll have learned that doing otherwise is counter-productive.