Child irritates me

I have a cousin who is 5 years old. He irritates me. I thought it was because I was pregnant, but I delivered a few days ago and I still feel the same. He is a very rude child. He steals stuff, you’ll literally tell him not to touch something and he looks at you and does it anyway, he fights my 2 yr old son for his toys and throws a tantrum when he doesn’t have his own way, he plays very destructively with my son’s toys so much that I told him to stop playing with them but he touches them anyway, he screams for stuff, he is just always in my face. I don’t usually feel this way towards kids, but I’ve literally never ever met a child like him. He does not listen to his parents unless they discipline him and I’m just over it. I feel so bad about it, but I can’t help how I feel about him. I love it when he’s not around. The house is so peaceful.