Offended?

I am not sure how to act in these situations as I have never been a mother before. Lately Owen has decided that when he doesnt get what he wants he can tell me that I am the meanest mom ever. Do I punish him for that or ignore it. I dont want him thinking he can talk to adults that way. He feels like he can say what ever he wants to me. That is just not happening.

For instance, this morning, he was putting his shoes on and all of a sudden decided that he wanted a different toy than one that he had picked out last week at the grocery store. When we were there he had the hardest time picking out what he wanted. He finally made is choice and I double checked with him to make sure. He was positive he wanted the two headed dragon instead of the octopus. Well today he has changed his mind. Had a little melt down, asked me to go get him the one he wants and I said no. So now I am the meanest mom ever and he is never sitting next to me again. With my hormones being the way they are I am somewhat offended. Usually it rolls off my shoulders. Today I am annoyed that he thinks he can talk that way to me. I feel like I do for this kid all the time and he doesnt ever remember. I know he doesnt mean what he says but I dont want to do things for him when he talks like that. So I sent him to his room and told him to come out when he could be nice.

Then he came out asking for gum. I said no, you dont speak to me like that and then get rewarded with gum. Which leads us to the next melt down and another and another. We have had a morning of melt downs. I feel like I am about to melt down. All of this because he decided he has changed his mind and wants a different toy.