Just try to feel me first. Was his father insane? He couldn't imagine a worse thing that someone invading your mind. It was worse than rape and murder; it was taking the thing that a human should value the most: his mind. He couldn't imagine how anyone could passively accept this.
He'd read all about compartimentalising and keep memories well separated, how to hide some memories and share others, but he didn't want anyone in his head for any reason. End of story. As soon as he felt his father, he knew that anyone trying would have to be a lot more subtle or brutal, because none of them would see anything.
That conviction made it easier to focus not to show how memories, but to push his father out. Even then he found the mental push to be tiring. "Fuck! I don't like that." Understatement of the year. "Are they likely to be obvious?" If they were, it might not be so bad. Kick them out and tell them to fuck off even if politely.