So today after work i went to the activity centre to pick up SS. 

What a surprised when i discovered SS was waiting with another little boy and his mother. 
The little boy was yonger than SS, probably 6 or 7 YO. He seemed eager to see me and said to SS : Is it her ? 
Then, he looked at me and said : i have something to tell you. His mother was just behind him. 

I did not understand what was going on. SS answered rapidly to me "No, he has nothing to tell you, let's go !" 

So i insist on the boy and asked him what was going on. The mother was quiet. 
He told me that SS has bullied him all the day, reffering to him as "Mister baby cuddly". His mother replied : "oh no my darling, i'm sure it was affectionate". 
I asked SS to explain himself. He said that the boy told him he has a comforter called "baby cuddly". SS thought it was funny and started to call him like this. Then, all the other kids followed.

I was so shocked. It's the first time for me to be pointed out by a child and his mother about SS bad behaviour. I didn't know what to say, so i came up with an "I'm sorry you feel hurt, i'm sure SS didn't mean to offend you but as you don't like it, i will tell SS to never ever call you like that". The boy was relieved, i asked his mother if everything was OK, and we left. 

I was so upset about SS behaviour. I didn't even know he was capable of bullying someone !
I was trying to figured out how to deal with that, when he naturally asked me while walking : "Are you pride of me ? You see, i didn't tell any bad lie about dad and you". I was just speechless ! 

I calmly answered : you just bullied a little boy, younger than you, all the day. He was so sad he waited with his mother to see and talk to me, and you are asking me if i'm proud of you ? No i'm not, there is nothing in your behaviour i could be proud of. Fortunately you're not telling bad lies about your dad and I. There is no congratulation for an absolutely NORMAL behavior ! Just stop asking for congratulation and start acting like someone who deserve it !

Then, he started all the victim speech : yes i know my behaviour is horrible. I've made really dangerous and serious mistake. I don't deserve any forgiveness for ever ever in my entire life.
I could see he didn't belive a word he was saying. He was just trying another method to be comforted and congratulated. 

I just don't know how to deal with his personality. I try my best to be a constructive model, but i just don't know what to do. I know he needs help, but, i'm just speechless.