I have an extremely angry kitten and I don't know why he's angry?

I have an almost 8 month old kitten, and since the day I got him when he was about 2 months, he has had a terrible temper. Whenever he meows, it's always a really angry meow or a demand, and if I'm holding him while he's meowing angrily, if I move him only slightly he hisses. But he's never clawed me, and has only bitten me when he wants to play. He is part Siamese (we think, because he has a long, lanky tail, a triangular-shaped face, and the irritating meow) even though he has orange fur. And the only person he likes is our other, older cat. Can anyone tell me why he is so angry, if he'll grow out of it, and what to do about it?