I can't tell you how many time my kids have said, "I hate you!", over the years. Or tried to hit me because they were angry with me. Or their dad, or sibling. This is a phase he is going thru. He has to learn how far he can go! He will grow out of it. Does he need discipline when he does it. Yes, he does sometimes. When he says mean things, sometimes, but not necessarily, just tell him you're sorry to hear that because you love him. If he's hitting etc, then, yes, he does need to be disciplined in some way. Time out, taking away a favorite toy, 5 minutes of quiet time in his room, not letting him watch his favorite tv show, no dessert after dinner. Something that will really impact him. Even if he acts like it doesn't bother him. My son was great at "pretending" he didn't care if I took away his favorite toy or sent him to his room. But I knew it did and he was upset about it. Sending him to his room seemed to work the best for me. He was trying to get attention most of the time when he was "bad" and making him go to his room really frustrated him because he no longer got my attention, he was alone with no ones attention except his own.
The most important thing is, you have to be consistent. If you punish him once for something, and he does it again, you have to punish him for it again and again. Do not let him wear you down. And dad has to also punish him for doing the same thing.
You also have to be consistent at praising him for when he does good things. Like if he tells you he loves you. Or puts his toys away when he is asked to. A big hug and kiss is sometimes all it takes. No matter what you are doing, it only takes a second but lasts forever in his mind and heart. This is how he will learn that being good is much better then being bad.