Why do some kidds have to be SO hard?

With Trace I can usually just talk to him and work with him to get cooperation. He is pretty moldable and wants to please us. Caden, on the other hand, I can't figure out! He wants our approval and love but doesn't seem to know (or care) how to get it. The past three days have been tough but this morning I finally lost it. He demands that I fix him an eggo without saying please or even asking me to do it. He pinches his brother for not answering him immediately then proceeds to call him names and mutter at him. All the while I'm in the front of the car telling him to STOP IT NOW. Doesn't care, just keeps at it. When I asked him to get ready for preschool he came back down with sweat pants. He knows we don't allow sweat pants to be worn to school and when I remind him his answer is, "well I want to be comfortable!" (Very disrespectfully) I told him to go upstairs and get a pair of pants that are appropriate for school. So he went upstairs and screamed at me that he doesn't have any pants that don't have holes in them - several times. When I got in the shower he sat at the bottom of the stairs the entire time screaming at the top of his lungs because he didn't know where I had put his sandwhich! (it was on the kitchen table).
I'll admit I finally lost it and gave him a little swat on the buns through his jeans. It didn't hurt him physically at all but I know it hurt his ego (which is apparently a little too big anyway!). So then I take him to preschool and on the way I told him that he was not going to watch any more Sponge Bob for a while. (his favorite show). I told him it is too disrespectful and until he can watch those shows and still be respectful then we wern't going to watch them. Well by the time I dropped him off it was obvious he had been crying and he was telling me he didn't feel good and didn't want to go. I felt terrible but I told him he had to anyway. I talked with him, gave him a hug and tried to get a laugh out of him with a tickle but he still walked away looking like the world was on his shoulders! I just don't know what to do with him any more. To ignore his behavior or try to talk to him only seems to make it worse. To spank or otherwise discipline seems to completely devestate him emotionally! Something has to be done though. Aaaaggghhh! Why oh why do some kids have to make life so hard!!???? I know this too shall pass, but I just really needed to get it off my shoulders!