If James had been surprised by his father's reaction, he might have been scared, but he was neither surprised or scared. Well, he wasn't anymore that is. It was different way back when he was a kid, but now he was 18 years old and Harry Potter was not scaring him at all. "Do you even realize how old I am!" he shouted back, forgetting he was at school and that his father was a teacher. After all, the man screaming at him wasn't doing so as Professor Potter but as Harry, James' father.
He would have been hurt at being called a slag if he had let it. "And before calling me a slag and telling me that you and Mum raised me better than that, can you just analyze the situation half a moment and maybe then you'd understand why I'm doing things the way I do!" his hands were shaking with anger as he, once again, ended up fighting with his father.
"Have you ever considered the fact that none of them actually cares about me other than liking the fact that I'm your son? I tried the whole girlfriend thing. It failed because I'm not you. I'm not some kind of younger version of you and she hated that." He breathed in deeply, a clear sign that he was actually trying to calm himself down. Do not think about Sam.. do NOT.
"What I'm thinking? I'm thinking like any other 18 year old bloke, that's what."