A.B.
LOL Well don't give up..he is only five... sounds to me that he could be getting a lot of it from the little girl. Is there anyway he can be paired with another boy? Little kids generally like to be with there own sex. I would get him involved with extra stuff like martial arts. They teach discipline plus he will be with his peers.
Keep showing affection....he may be a little upset over the whole kindergarten thing. Good for you to not want to take his disrespectful attitude though...nip that now while you can.
Good luck!!