Is it normal to feel animosity for no reason?

I get these feelings of animosity for no reason sometimes. Or I think there is a reason its just I have a hard time distinguishing what it is exactly. Usually its because I sense people don't like me or think bad of me right away. That can be an insecure issue or I just sense things quickly. I think its 50/50. But yeah once I sense that, I obviously don't want to associate with those people and when I have to, my animosity can show through attitude or the looks or vibe I give to them. A really good example are my brother's friends. He passed away but when he was alive, they would all hang out and not with me. Supposedly I seemed like the out cast and then once he passed away, his friends look at me like in a bad way as if I don't care about what happened, or I am the out cast sister blah blah. It is so annoying because they don't even know me. And when they talk to me, I'll be as polite as I can be but I have a little attitude going on because I know they don't think positive of me as if they know who I am, and my side of the story. So I dread whenever it comes to these events celebrating my brother's birthday or the date he passed away because i know there will be a bunch of people there I don't like because they don't like me. There's just tension overall and I just want to get away because I get disgusted with those people.