1) "No."
2) "I said no, and this discussion is over, my answer is final, do not ask again."
3) Warning: "Next time you ask me this, you'll be on timeout."
4) Timeout
I agree with this, but I will mention that I have learned to read my daughter fairly well. If I can tell that a "No" response will lead us down a path I don't want to go down, and if I can accommodate her much more easily, then I often pick the path of least resistance right from the beginning. I'll never contradict my initial answer, but I'll agree to things I don't really like sometimes, just to placate her. (I obviously wont agree to anything dangerous though.)
Another thing I would like to mention is that different people react differently to children crying. I personally can't stand it. It really drives me insane. I have to use something to drown it out, or else I think I'd break down in tears myself. My wife doesn't seem too bothered by it, though. On the other hand, I don't mind so much when my daughter wastes food, but that drives my wife up the wall.
So in some ways, the question isn't necessarily restricted to what to do with your child, but what to do with yourself that will allow you to do the right thing with your child.
Have you discussed this with your pediatrician?
Also, have you considered teaching your son sign language? We stopped using it once my daughter's spoken vocabulary took off, but there was a while there where she would use signs during times when she was too upset to speak. (Strange people and places can still make her go mute... but it's rare now, and she's forgotten all her signs.)
