Hi.....been there and done that.

I think that the best thing you can do is to try to disengage yourself from any arguments that may be ensuing. Seems like so long as he has a willing and able participant this will continue. I would come up with a one liner statement that gives your son a clear message that you are not going to engage in his conversation when he starts in. Something like, "Johnny drop it...I am not going down this road again with you." and then walk away. If he continues to badger you then tell him that he is invading your personal space and to leave. If he doesn't then go to the bathroom and remove yourself from his presence. Be consistent with this and after a while he WILL get the message.
It sounds as if your son may be hypomanic....during this time their behavior takes on an attitude that they know what is right for them and no matter how they go about it getting it is their goal. It is a grandiosity of thinking that they are above everybody else and it's their way of thinking and nothing else.
You didn't mention his meds but perhaps it is time to bring this to his doctor's attention so that he can make some adjustments that may help out with this behavior.
I hope that this helps you some....I remember the days when EVERYTHING was an argument....I could say the sky is blue and to her it was definitely grey.

It's easier if you just let these things bounce off of you.
You sound like a wonderful mom and your son is lucky to have you. Hang in there and feel free to come here with any of your concerns....there are other moms here who have teens with BP who will be able to help you out with similar situations that we experience. My daughter is 15 and we are still fairly new to all of this and it is definitely a challenge in terms of learning how to best handle things as well as as finding the right meds. And even when you do, things could be offset so easily requiring an adjustment in meds.
Again welcome and I hope that things get better for you and your son. It definitely is an up and down experience for the child as well as those who love him/her. Nobody knows that more than a parent of a child with BP.
((((HUGS)))) ~ Goody