A mother's worst fear...

So there are some things that every mother fears. There are 3 words that can bring anger at the moment and tears later that night...  It usually happens to all mothers... At least someday. 
And my day just so happened to be today. 
The 3 words I dread, I hate you. 
Yes, my three year old son, told me he hates me. 
It was nap time, and had been an early morning, and we were heading upstairs to go ni-night. 
Well he decides he wants cheese, I said later. And the tears started flowing. So I said son no, go potty it is time to take a nap. And he says "Mommy I'm mad I hate you" Waaaahhhhh....
SoI say what did you say, because I am thinking to myself, there is no way this kid just said this to me. And he says I dunno. Finally get him to tell the truth... So I yelled, got mad, layed him down in bed and then walked in the bathroom where I saw the soap. 
So I walked back into his room and made him taste it and told him the next time he ever, ever says that to me or ever talks back to me, 
He will eat soap. 
So now needless to say, he has a little fear of soap. 
Hopefully this doesn't become one of those weird fears that grown up's have that they remember from their past and he just cant understand why he is so afraid of soap because then I might feel bad. 
So yah, that was my fun day. 
Where do kids learn these things??
I know I dont ever say that. I have never said it to him or to anyone else around him. And he just pops out with it all of a sudden. He kept saying from his friend but the kid has been out of daycare for months now... 
Oh boy.