Originally Posted by
Del Murder
If you watch the Brotherhood episode about him, it explains a little bit of how he can be such a dick to Noctis. However, (1) you shouldn't need a separate anime to explain the motivation of your game's characters and (2) they've been together for several years after that so it was still odd that he went right back to dick mode after Altissia. It's not like Noct sat on the sidelines during Altissia, he was pretty active and suffered a pretty big loss.
One thing that bothered me in the whole game was that if Noctis bumps into him while running around, he gets very snippy with a 'hey watch it!!' which doesn't seem like a good way to talk to one of your best friends.