"yes he is rude because when he walks into a room he wont say hi to everyone unless you call him out on it or you have something he wants like candy or money and he intentionally scares my little ones and my nefews that are only 2 and thinks he is doing no wrong by looking at them with evil eyes."
These things are totally normal for an 11 yr old boy.
They need to be taught to say hi, But EVERYTIME they walk into a room? Why? We do not do that in our home.
The teasing and trying to scare the younger cousins is also normal, but instead of making it into a bog deal, just remind him, "they are only 2, so teasing them and making scary faces at them, scares them a lot longer than if they were your age.."
If he has never had older siblings or younger siblings all of this is new to him.. How to play with way younger kids.
It also seems like your expectations are your own secret until he does something you do not like and then you take it way out of proportion. (The hi every time he walks into a room)
Children need guidance not a hammer over their head or feelings.
Remember when you correct a child, you do not want to make them defensive or embarrassed, you want save some of their dignity..
"I am sure you do not realize his, but scary faces to a really young child is super scary." "Your cousins look you up to you, you do not want them to be afraid of you."
"Remember they are only 2, so be a little careful with them., I know you do not want to accidentally hurt them."
Take a step back and imagine you are only visiting a home every once in a while, but one of the people was always correcting your behavior.. It is pretty stressful.
I am a child of divorce and going back and forth to my own home and my dads new home with his new wife was very stressful. She had never had children of her own and had expectations of manners and behaviors.. Way more formal than our own home. We ALWAYS felt like guests, because we could never just be ourselves with out a suggestion or a critique. My stepmom NEVER changed, but we were expected to always change our behaviors in "her house".