I'm annoyed at my cousin for thinking out loud
Is he saying something offensive?
No, he thinks aloud and that makes me want to smack his head.
It is understandable that you get annoyed when people talk aloud. It stops you from being able to think yourself.
He thinks aloud because he doesn't have any smart people to talk to.
I suggest someone introduce him to the smartest people they know. He is not getting far with talking out loud to make up for it. That does seem somewhat odd and disturbs the way other people look at him.