^^^Going by that argument though, Spock had only just previously been mind melding with his former superior officer, arguably the man who gave him a chance on a ship and elevated him from an academy lecturer - as he died, and displayed absolutely zero emotional reaction. Contrast that with butting heads with Kirk after Kirk saved his life, after going on the mission to catch Harrison and agreeing to work with Harrison and I just can't see any basis for a friendship there that I can believe in. Or at least one which would cause that level of a psychotic break. I think there is a middle ground at the end of that scene I could have lived with, but Spock screaming "KHAAAAN!" the way he did was absolutely comical. Even when his mother died and home planet got destroyed, he had to be goaded into being angry. The cause and effect of his anger over Kirk's death just doesn't add up to me. :/
Remember, that Pike's meld was the very first time Spock had ever melded with someone at the moment of their death. It's the equivalent of emotional overload. He even spoke of the confusion involved.
When Kirk was dying, all of these impressions he received from Pike's death dropped on him like a ton of bricks, and even without melding with Kirk, he felt everything his friend was experiencing. It was the empathy Kirk had been trying to show him from day one, that finally reached him, and it overloaded his emotional barriers.
As for his mother, that's just shock, and the need to be A Good And Proper Vulcan™. We also saw him suffering for it later, but he also had Uhura to help him through it.
Fair enough.
They still could've done a better take of "KhaaAAAaaaan!" though :P