Why is my brother always angry?

My twin brother is always mad and angry at everybody me, family, and even his girlfriend. he is only nice when he wants something and even then he can be an .he always try's to find things people are doing wrong and yell's and complains about it weather its your drinking to loud chewing to loud typing to loud just basically anything he could possibly see and complain about he does. He's 19 male doesn't drink, smoke, and doesn't do any drugs, he's the good looking one (so its not from that), an aspiring cop(go fig a cop that's an hole).he has been like this for a year or 2 but it has gotten a lot worse in the past couple of months it might be because he caused our house fire(left a pot of oil on the stove). There is no talking to him and he can never be wrong. WTF is wrong with him or is he just an ?