Teen mood

It was a good day of revision, as I revised so much for one subject. But after revising, I just realised that it's not that much, only one chapter minus a page which is equivalent to one lecture.
Argh! My brother was being so rude today whilst I was on the phone. I was just talking on the phone in the living room, then my brother comes into the room and says to me to go away as he wants to watch tv. But the only thing I thought was weird is that he always goes into his room when he's about to eat except for today.
I said: "no as I'm tired and I am on the phone".
brother: "So it's handheld so go away. I want to watch tv".
Me to A(on the phone): "Just ignore my brother as I was here first"
brother: LALALALALALALALALALALA!!! (very loud)
Me: brother, please be quiet! I'm on the phone!
brother: No you move, I want to watch tv! LALALALALALALA!! (continuing to shout out loud)
Me to A: "Sorry, my brother isn't usually like this. He has never been like this, only this time"
brother: LALALALALALALALALALALALALALA!!!
A to Me: "Just move away as I am getting a earache from hearing him"
(I had to move to my room)... >.>

I don't get it, he's 17 years old. Also, he wasn't watching anything that great that he wants to watch, just random channels. So why this time he decided to act like a spoilt brat? I know I was rude for not moving away, but it's happened before that I was on the phone and yet he would just eat upstairs with his food. I think the teenager mood is kicking in at the moment.