How did you correct your young child when they started getting that teen-like attitude?

My son will be 4 in 2 months. He's kinda always had an attitude (probable got it from me), but I've been able to correct it easily by simply saying no or giving him a time out etc. By lately he really has MAJOR attitude and is SO rebellious and talking back. He learned (probably from another child at day care) how to spit at people and I give him a warning then when he does it again he gets a time out, but he will just keep doing other things like saying "don't talk to me! you're not my friend!" or sticking his tongue out or whatever. He seems like a 14 year old stuck in a 3 year olds body. LOL Looking for advice on how to nip it in the bud now before it gets out of hand.