How do you stop your brother from being an ass

Not all siblings get a long and sometimes it takes until people get older to start getting along.  There are of course the sad situations in which siblings never learn to get along.  However, I would just try to respect what he wants from you, whether it's to leave him alone or to help him with something, whatever.  Try to get on his good side, and when he starts being an ass to you, remind him nicely of the nice things you've done for him.  Try to just have nice interactions and to avoid the situations in which you guys don't get along well.  Be considerate and hopefully he will reciprocate.  Good luck.

Try sharing some personal dilemmas with him . I believe if you come forward with a true problem and he'll see he is your only option he might soften up a bit. In these cases time is the best remedy. Is itt just the two of you?

You cannot stop it totally but you can do something that can made him share to you why he do such foolish things.. I have a brother and he really gave me a lot of headaches.. but I'm trying to be calm as ever to show him that I don't need a fight from him..*sometimes I yelled that I almost wanted to give him a hard pinch on the face* what I need is for me to understand him why he become like that.. sometimes there are cruel things or pain  that happened to a certain person and they didn't know how to express it, sometimes they are scared to tell it.. what they need is space.. a total understanding that even he still made you really mad.. he knows that you were there for him.. and time will come he will become fed up of the fight and he will realize one day that I must move on and change for the better.. that was what exactly what happen to my brother and I was really happy for him.. hope he really changed for good...