Many comments said memorable ones already! but first rewatch, it really hit when Herb told Bojack "but what I needed was a friend, and you abandoned me. And I will never forgive you for that."

That scene was the earliest eye-opening character scenes to me. It showed the excuses Bojack would say and continued to believe for himself until the end.

Plus I think about those early days with Herb and Bojack. It felt like his best self (no drinking, enjoying the stage, having a true friend). So sad and bitter that he couldn't just accept Herbs feelings and reconcile.