how do i get my son to stop hurting himself when anyone tells him "no"?

Ignore him. Or when he wants something use a different phrase like "not right now",or something along those lines.

I would try very hard to use different language. I, personally, would NOT ignore him. Children really don't respond well to being ignored, especially when they are crying out for comfort. Kids hear 'no' a thousand times a day, try to put yourself in his shoes, if you were told 'no' as often as him you would probably lash out in some way too. If he asks for something he can't have use a positive instead "Well, we can't really have cookies right now, but we CAN have a banana" or "Oh hitting your sister isn't nice, here you can hit this pillow..boom boom-isn't than fun!?" See how you can take what would be a "no" and make it into something positive? Save your "no's" for big things. I started this with my dd, I was saying 'no' to her so often the word began to lose any meaning. Now we always look for a positive. We are all much happier now!